Select the tabs below to:

  • Find out why we age.
  • Explore viewpoints on aging from Koshland Science Museum Visitors.
  • Learn about the development associated with different stages of life.
  • Find out how changes to vision, risk perceptions, and experience affect driving.

Why Do We Age?


Explore the videos below to watch different Koshland Science Museum visitors describe their answers to the following six questions:

What was the happiest moment of your life?

What are the most important lessons you’ve learned in life?

What is your earliest memory? How old were you?

Are there any words of wisdom you’d like to pass along?

How has your life been different from what you imagined?

What does your future hold?

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Developmental Stages

Learn about the following developmental stages, their definitions, and the physical; cognitive; and emotional, cultural, and social development associated with each.


Pre•na•tal \ ()prē-nā-təl\


Definition: occurring, existing, or performed before birth <prenatal care> (Merriam-Webster Online)

Conception to Birth

Physical Development

  • Nature and nurture are both important in the development of all stages of human life.  Nurture, that is, environmental factors, such as good nutritional intake by the mother and the avoidance of toxins, significantly affect prenatal health. Nature, or genes that may cause disorders, also influence prenatal development.
  • We start as a single cell that contains all the genetic information that we will need for our entire life.  From that single cell, 350 different cell types will be formed prior to birth.
  • Prenatal development spans three stages. Gestation begins with conception and lasts until the fertilized egg is implanted in the uterus (around two weeks). The embryonic stage marks the development of the major organs and limbs (two weeks to ten weeks after conception). The fetal stage lasts from the eleventh week to birth.  During this stage the development of all organs continues and the fetus grows in size and weight.
  • Environmental factors pose risks at different stages of development. For example, the embryo is particularly vulnerable to the effects of German measles (rubella). The mother’s infection by the virus during the first month of pregnancy leads to an almost 50% chance of infant blindness or brain damage. The percentage drops to 22% if contracted in the second month and decreases thereafter.

Cognitive Development

  • Executive function refers to a variety of interdependent skills that are necessary to perform goal-directed activities such as making plans and purposefully integrating past knowledge and present information. It had been believed that such skills were not expressed until later in our development, such as during adolescence. However, evidence indicates that cognition begins to develop as early as in the womb.
  • Our cognitive development is influenced by our prenatal environment.  A healthy fetus requires oxygen, protein and micronutrients. Conversely, the absorption of toxins such as alcohol, lead and tobacco can have negative neurological effects that last a lifetime.
  • The baby’s physical environment has the strongest effect on its prenatal development. There is no evidence that non-physical stimuli such as exposing the baby to classical music in utero will raise a child’s IQ.


In•fant \’in-fənt\


Definition: 1. A child in the first period of life, 2. A person who is not of full age:  MINOR (Merriam-Webster Online)

Birth–18 months

Physical Development

  • Immediately after birth an infant will normally lose some baby weight, but after 2 weeks the infant starts gaining weight quickly. By 4 to 6 months, the infant’s weight should be about double its birth weight.
  • The head and neck of a newborn account for about 30% of its total body volume. In an adult, the head and neck account for about 10% of our total body volume.
  • An infant’s physical characteristics change rapidly.  Until about 2 months of age, a newborn cannot support its head or control its hands or feet.  This changes by 4 months when an infant can begin to manipulate its hands and feet, and the neck muscles are strong enough to hold the head upright.
  • By 9 months, the infant may have begun to crawl, can possibly walk with support from an adult, and can sit without support for a long period of time. At one year, the infant may be able to stand and begin to walk alone.
  • Synaptic overproduction and loss, a process in which neurons are produced quickly and pared away, is a critical aspect of brain development. This process is most active during the first year of life, but can extend into adolescence. Different brain regions appear to develop at different rates. For example, neuronal development in the visual area of the brain peaks halfway through the first year and reaches adult levels around the end of preschool.

Cognitive Development

  • Some heritable genetic disorders that cause cognitive impairment can be prevented.  For example, damage due to phenylketonuria, a heritable disorder that leads to mental disability, can be completely prevented by  following a strict diet avoiding the amino acid phenylalanine, which is found in many foods including eggs and milk.
  • Infants have a surprisingly sophisticated understanding of the world. At less than a month of age an infant can imitate another’s gestures and by nine months may learn new behaviors through simple observation. For instance, infants have remembered how to unlock a container up to 24 hours after watching a peer do it.
  • Loving care-giving can enhance certain neurochemicals—such as serotonin and thyroid hormones—that help regulate distress and pain.  This has been shown to affect a person’s brain chemistry throughout his or her life.
  • Infants raised in a healthy environment—with access to quality education, care giving and nutrition— score significantly higher on IQ tests. In contrast, infants raised around harmful toxins—such as cigarette smoke and polluted air—are more likely to experience cognitive impairment later in life.
Emotional, Cultural, and Social Development
  • By 6 to 9 months, infants are interacting with their social environment. Babies will smile and babble at other babies, and sometimes initiate or return social bids. By 9 to 12 months, infants will imitate each other as a simple form of play.
  • Children tend to say their first words at between 10 and 15 months. Following this, they learn that words can be broken into parts, such as how “shoes” can be broken into “shoe” + “s”, eventually combining words into meaningful phrases.

Toddler & Preschool

Tod•dler \’täd-lər, ‘tä-dəl-ər\


Definition: one that toddles; especially: a young child. (Merriam-Webster Online)

Pre•school \’prē-,skül, (,)prē-‘\


Definition: of, relating to, or constituting the period in a child's life that ordinarily precedes attendance at elementary school. (Merriam-Webster Online)

19 months–5 years

Physical Development

  • By two years old, both boys and girls stand about 2 ft. 10 in. tall and weigh between 27 and 28 pounds. Growth rate and weight gain remain relatively constant. The child will gain approximately 5 pounds a year until the age of 5.
  • The child typically acquires large motor skills allowing him or her to stand and walk. During preschool children become more skilled at running, jumping and kicking, and will commonly be able to catch a ball, pedal a bike and hop on one foot.
  • Fine motor skills develop during this stage. The child can stack objects and will learn to scribble, use a spoon and cup and copy a circle. By the end of preschool the child will have the motor skills for better self care, including dressing and neatly feeding him or herself during a meal.

Cognitive Development

  • Toddlers notice others’ states and activities. They are able learn from others, perceive goals and reproduce strategies to achieve those goals. Toddlers may recognize that others may have different tastes or preferences that influence how goals are achieved.
  • Cognitive development in toddlers may suffer by being too parent-dependent. Intrusion from parents and teachers can discourage mastery of behavior, whereby toddlers propel their own personal growth.
  • Academic performance during the preschool years is often predictive of success throughout life.  Thus it is important that children struggling academically be helped as soon as possible. Programs that sustain and improve the quality of education for at-risk preschoolers are critical.
  • The ability to self-regulate, sequence, plan, and organize to achieve goals becomes expected. Deficits in these abilities can result in long-term deficits in social and emotional development.

Emotional, Cultural, and Social Development

  • The toddler who has learned that the people she depends on for comfort will help her when she is emotionally distressed is more likely to approach others with empathy and trust than the toddler whose worries and fears have been dismissed or belittled.
  • Toddlers self-regulate their emotions. Children talk to themselves to give encouragement, change goals when frustrated, and employ other strategies to avoid distressing situations.
  • Shyness is a trait that parents and caregivers may alter. Many preschoolers who are initially shy do not remain so. Unique patterns of brain activity in children who do not develop beyond their initial inhibitions suggest the presence of an underlying influence on social behavior.
  • Almost all children will learn to talk without explicit instruction. Children born into bilingual homes appear to learn each language as if it is their only tongue. A problem bilingual children encounter is retaining both languages when one language is used in the home and the other is used in the broader society, such as by teachers and peers.
  • While almost all children will learn to talk, not all children will read.  Writing requires more self-conscious teaching than spoken language, and not every child will reach a fluent reading level in his or her lifetime.

School Age



Definition: old enough to go to school <school–age children> (Merriam-Webster Online)

6 years–12 years

Physical Development

  • By this age, large motor skills are advanced, but coordination, endurance, balance and physical ability vary.
  • The degree of fine motor skills varies widely among school-age children. This variance can affect the child’s relative ability to write neatly, dress appropriately and perform other household chores.
  • Weight, height, and body build differences between children at school age become more pronounced.  While some children may be genetically predisposed to being taller, shorter, or having a certain body type, external influences—such as nutrition and physical exercise—can change these outcomes. Puberty may start at the age of 9, triggering a growth spurt.

Cognitive Development

  • When a person reaches school age, cognitive growth accelerates. Many of the core functions of cognitive health—such as executive function and speed of information processing—expand very quickly.  Six-year-olds have performed as well as adults on tasks involving visual searches and arranging simple sequences.
  • Early learning capabilities can remain intact within adverse circumstances and environments. Children showing early delays in learning or cognitive performance can benefit from family-centered, community-based support that is individualized to the child’s needs. One exception to this resiliency is attention. Due to the importance of attention to school achievement, problems in attention need to be identified and tended to early.

Emotional Development

  • Early school years are often seen as a carefree time, but disappointments, frustrations and hurt feelings are also inevitable aspects being young. During school age, finding ways to regulate emotions is critical to managing these negative feelings.
  • The ability to regulate emotions is linked to social development, allowing a child to more easily relate to others at home, at school, and on the playground. Emotional control prevents outbursts and withdrawals from stressful situations, which can make social development difficult.

Cultural and Social Development

  • The ability to learn some aspects of language—such as how prefixes and suffixes can change a word’s meaning—seems to decline after age seven. Because of this, late-learners of language may not achieve native-like competence in language.
  • Serious behavior problems are seen in 5 to 10 percent of school-age children.  These behavior problems are strongly associated with problems related to schoolwork, which can in turn aggravate behavioral problems.  Early interventions that focus on multiple settings, such as home and school, can help to break this cycle.
  • While many factors are associated with the early emergence of negative social behavior, not much is known about the factors that promote or prevent continued bad behavior, although peer groups seem to play a role in behavior among older children. Peers can expose others to negative social behaviors such as delinquency and drug use and change attitudes towards those behaviors.

Adolescent & Young Adult

ad•o•les•cence \,a-də-‘le-sən(t)s\


Definition: 1. the state or process of growing up, 2. the period of life from puberty to maturity terminating legally at the age of majority, 3. a stage of development (as of a language or culture) prior to maturity. (Merriam-Webster Online)

Young Adult


Definition: 1. a teenager (used especially by publishers and librarians), 2. a person in the early years of adulthood. (, based on Random House Dictionary)

13 years–34 years

Physical Development

  • Puberty brings about physical maturity and a final growth spurt. The child’s nutritional needs increase to reflect a rapidly growing body.
  • Girls may begin to develop breasts as early as 8, but typically develop fully between the ages of 12 and 18. Hair grows and reaches its adult pattern around the age of 13 or 14. The growth spurt for girls typically occurs between the ages of nine and 15.
  • Boys begin to notice testicle and scrotum growth around the age of nine, reaching adult size and shape around 16 or 17. Pubic hair, armpit, leg, chest, and facial hair begin to grow at around age 12 and reach adult patterns around 15 or 16 years. Boy’s voices change during puberty.
  • After puberty, aging begins. Approximately 50% of men will show signs of baldness by the time they reach 30 years of age.  Hearing loss begins, but it typically becomes noticeable only after the age of 50.

Cognitive Development

  • Teens who do not complete high school are more likely to display destructive behaviors in adulthood., including substance abuse, criminality and delinquency, and to experience unemployment and low income.
  • Self-regulation and impulse control steadily improves into adulthood, but risk taking increases during adolescence. Rates of injury in adolescents increase by nearly 200% from childhood.
  • During adolescence, the ability to plan and carry out new and complex sequences of actions reaches maturity.
  • People who receive higher levels of education are less likely to develop dementia later in life. Researchers speculate that those who pursue higher education tend to place themselves in more cognitively stimulating environments throughout life.

Emotional Development

  • By adolescence, the ability to control emotions should be fully developed, but the magnitude of that control varies across individuals. Determining when help is needed is often difficult because some teens simply require more time to grow up than others, eventually reaching a healthy degree of maturity and self-control later in adulthood.

Cultural and Social Development

  • Teenagers are often described as “risk takers.” Research, indicates that though teenagers may not be more inclined to take risks, they are not good at identifying risky situations. Strategies to curb risky behavior may need to be revised to improve adolescents’ skills at recognizing risk.
  • Teenage willingness to take risks can be intensified by the teenager’s social environment. The more times a teenager has been exposed to risky behaviors, whether through experience or the accounts of friends, the less risk that teenager associates with dangerous activity.
  • During early adulthood, leisure time decreases as individuals take on more important responsibilities at work and at home. Young adulthood is customarily seen as the appropriate age to start full-time jobs, get married, and have children.
  • Evidence indicates that parents can prepare their children for new social challenges—such as the dangers of binge drinking on college campuses—by discussing the topic with their children prior to college.


Adult \ə-‘dəlt, ‘a-,dəlt\


Adulthood = noun

Definition, Adult:  fully developed and mature:  grown-up. (Merriam-Webster Online)

35 years–55 or 65 years

Physical Development

  • Aging begins as soon as one reaches adulthood and is as much a stage of human life as are infancy, childhood and adolescence.
  • Each of us experiences aging differently, with various organs and systems aging at different rates among individuals.
  • The sharpness of the senses starts to decline as a result of aging. Eyes become drier and the pupils decrease in size. By 60 years of age, the pupils will be 1/3 their size when the person was 20. The number of taste buds begins to decrease between the ages of 40 to 50 in women and 50 to 60 in men.
  • Without exercise, muscle mass can decline 22% for women and 23% for men between the ages of 30 and 70. Exercise can slow this rate of loss.

Cognitive Development

  • The adult brain has a much greater capacity for growth and change than previously believed. The adult brain can grow new dendrites, make new connections and pathways, and perhaps even create new neurons.
  • On average, skills in verbal meaning, spatial reasoning, numbers, and word fluency increase until we are in our late 30s, remain stable until the early 60s, and decline thereafter. Base cognitive skills such as perceptual speed and verbal memory have a similar life course.
  • Cognitive stimulation can help delay the onset of Alzheimer’s disease in affected individuals and slow its progression after onset.

Emotional Development

  • Adults report less distance between their ideal self and actual self, indicating that as people develop into adults they become more satisfied with who they are.
  • Multiple studies have shown that older individuals tend to experience fewer negative emotions than their younger counterparts. Even after a traumatic event, adults and older adults cope better than do younger people.

Cultural and Social Development

  • Social development can change suddenly through life-changing events such as becoming a parent or losing a loved one, as well as gradually through social environmental factors such as advancement through a career.
  • Despite the significant social changes experienced during adulthood, an individual’s underlying personality remains fundamentally unaltered. Adults adapt their preexisting personality to their changing circumstances.
  • During late adulthood, adults tend to engage in a social pruning process. We keep emotionally close social relationships while allowing more peripheral relationships fade away.

Old Age

Old \’ōld\


Definition: advanced in years or age <an old person>. (Merriam-Webster Online).

Fifty-five or 65 years and older

Physical Development

  • Old age can be broken into three stages: young old (55–65 years of age), middle old (66–85), and old old (85 and older).
  • The bones become more brittle as they lose calcium and other minerals. Similarly, joints become less flexible as the joints lose fluid and cartilage begins to rub together.
  • Though the degree of vision impairment varies among individuals, almost everyone over fifty-five will need glasses at least part of the time.  The most common visual difficulty at this age is focusing on things very close.
  • In old age, sense of touch starts to decline. This decreased ability to detect vibration and pressure may result in injury. In fact, many older people have a reduced sensitivity to pain.
  • Older people are more susceptible to chronic diseases such as diabetes, lung disease, arthritis, and hypertension.

Cognitive Development

  • Evidence indicates that older individuals can train specific, but not general, areas of cognition. Memory training, for instance, has been effective for adults in their 60s through 80s.
  • Physical training can also improve cognition in old age. Research has shown that exercise can enhance brain function and delay brain atrophy.
  • Despite general declines in cognitive performance in old age, reasoning as it applies to complex matters of daily life seems relatively unaffected by normal aging.
  • Cognitive functions such as memory, spatial processing, and attention may decline at different rates among people and within individuals. The rate of decline of a particular function in one person is unlikely to match its rate of decline in another.
  • Technology can help counter the effects of cognitive decline.  For example, computer-aided sensors are being used in cars to detect rear obstructions that older people may have difficulty seeing.

Emotional Development

  • Older more than younger adults are more likely to pursue emotionally meaningful goals. Younger adults tend to pursue goals that expand their horizons or generate new social contacts. As we age, our goals change to accommodate changes in our resources and in our physical selves.
  • Views of the self during aging may influence the course of aging. In a study of people 50 to 94, people with strong, positive attitudes toward the aging self tended to live, on average, 7.5 years longer than those with negative attitudes.

Cultural and Social Development

  • In the United States during the 20th century, the average retirement age fell from 74 to 63.
  • As we age, our social networks tend to shrink and a larger proportion of one’s social network becomes comprised of emotionally close partners. This change in social habits reflects emotional development in old age, where individuals begin prioritizing emotional goals.

Driving at Different Ages

The leading cause of death for Americans aged 5-34 is motor vehicle accidents. Driver behavior has been identified as the major factor in approximately 90 % of roadway accidents.  Learn more about the factors that can affect driving in the following videos.

Teen Driving

Motor vehicle accidents are the leading cause of death for U.S. teenagers, accounting for more than one in three deaths in this age group. What factors make driving so deadly for teens?

Older Drivers

In the United States, driving is the most common form of transportation for adults over 65. Unfortunately, per miles spent behind the wheel, they are disproportionately at risk for accidents. It is not clear at what age a person becomes an “older driver.” However, a number of studies show significant differences between the driving skills of relatively older versus younger drivers.