Physical development of young adulthood

Updated February 21, 2017

Young adulthood is generally considered to occur between the ages of 20 and 40 (ref 1), as opposed to middle age, which occurs between 40 and 65 years. (ref 2) According to the U.S. Census Bureau, 23.7 per cent of the population was between the ages of 18 and 35 in 2001 and 6.9 per cent was between the ages of 20 and 24. (resource 1)

In the Prime of Life

Young adulthood is the healthiest time of life for most individuals, according to Carole Lium Edelman and Carol Lynn Mandle, authors of "Health Promotion Throughout the Lifespan." Men achieve full height and growth by about 21, while women achieve this by about 17. Muscle strength and manual dexterity peak between 25 and 30 (resource 1), while internal organs and body systems are at full maturity, functioning at peak efficiency. Young adults visit their doctors and are admitted to hospitals less than at any other stage of their lives; even the common cold is less common at this time. (ref 1)


Fertility peaks in young adulthood. Assuming they are healthy and are with healthy, fertile partners, women engaged in unprotected sex have a 50 per cent chance of achieving pregnancy between the ages of 19 and 26 in any given menstrual cycle, while women between the ages of 27 and 34 have a 40 per cent chance of pregnancy given the same circumstances and those between the ages of 35 and 39 have a 30 per cent chance. (ref 1) If fertility issues do occur during young adulthood, they are generally due to low sperm counts and blocked Fallopian tubes. (ref 3)

Factors Affecting Physical Development and Health

Lifestyle choices begin to affect physical health and optimal development during young adulthood. Diet, obesity, exercise levels, smoking and substance abuse are examples of such consequential lifestyle choices that can determine whether a young adult reaches full physical developmental potential. Income and educational levels tend to affect overall health status at this stage and minorities are more likely to be less healthy largely due to statistically lower quality health care. Social relationships, especially marriage, are linked with better physical and mental health in young adulthood. (ref 3)

Specific Health Concerns

Specific health conditions or occurrences can drastically affect overall health, optimal physical development and survival during young adulthood. The leading causes of death, from the most common to the less common, are accidents, cancer, heart disease, suicide, AIDS and homicide. (ref 3) Health care professionals during this stage of life focus on optimising a patient's health through good health habits (such as exercise and diet) and recognising early signs of chronic or debilitating diseases. (resource 1)

Signs of Aging

Signs of ageing begin to appear in a young adult's thirties. Wrinkles, sagging skin and greying or thinning hair are some of the more noticeable cosmetic indications of growing older. (ref 1) Flexibility begins to decrease (ref 2) and muscle strength declines by around 10 per cent per year between the ages of 30 and 60. Manual dexterity also begins to decline in the mid-thirties. (resource 1) However, lifestyle can affect this ageing process; a fit 40-year old can outperform a sedentary 20-year old. (ref 2)

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About the Author

Elizabeth Jennings began publishing creative works in 1988 and has been a professional editor and writer since 2002. She holds a dual Bachelor of Arts in anthropology and philosophy.