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Physical Growth and Sexual Maturation of Adolescents
During adolescence (usually considered age 10 to the late teens or early 20s), boys and girls reach adult height and weight and undergo sexual maturation (see Puberty in Boys and see Puberty in Girls). The timing and speed with which these changes occur vary and are affected by both heredity and environment.
There is a growth spurt during adolescence. The growth spurt in boys occurs during mid-adolescence between the ages of 12 years and 17 years and usually begins a year after the testes start enlarging. Boys grow about 4 inches (about 10 centimeters) during their year of maximum growth. The growth spurt in girls occurs in early adolescence between the ages of 9½ years and 14½ years. Girls grow about 3½ inches (about 9 centimeters) during their year of maximum growth. In general, boys become heavier and taller than girls. By age 18, boys have about ¾ inch (about 2 centimeters) of growth remaining and girls have slightly less.
If the timing of growth is not typical, particularly in a boy whose physical development is delayed or a girl whose development occurs early, emotional stress is likely. Most boys who grow slowly eventually attain normal height. However, adolescents whose growth is delayed or abnormal (see Short Stature) should be evaluated to rule out diseases and other physical causes and be given reassurance if the evaluation is negative.
Sexual maturation begins at different ages depending on genetic and environmental factors. Sexual maturity begins earlier today than a century ago, probably because of improvements in nutrition, general health, and living conditions. For example, the average age that girls begin menstruating has decreased by about 3 years over the past 100 years. However, whenever sexual maturation begins, it typically occurs in the same order.
In boys, sexual changes begin (see Figure: Milestones in Sexual Development) with enlargement of the scrotum and testes, followed by lengthening of the penis. Next, pubic hair appears. Armpit and facial hair appears about 2 years after pubic hair. The growth spurt usually begins a year after the testes start enlarging. Boys in the United States typically have their first ejaculation between 12½ years and 14 years of age, about 1 year after penis growth accelerates. Young adolescent boys often have slight enlargement of the breasts that usually resolves within several years.
In most girls, breast budding is the first sign of sexual maturation (see Figure: Milestones in Sexual Development), followed closely by the start of the growth spurt. Shortly after that, pubic and armpit hair appears. Menstruation typically begins about 2 years after breast development starts and when growth in height slows after reaching its peak velocity. In the United States, most girls start their period at 12 or 13 years of age, but there is a wide range.
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