PHYSICAL DEVELOPMENT
During adolescence, young people go through many changes as they move from childhood into physical maturity. Early, prepubescent changes occur when the secondary sexual characteristics appear.
Girls:
- Girls may begin to develop breast buds as early as 8 years old. Breasts develop fully between ages 12 and 18.
- Pubic hair, armpit and leg hair usually begin to grow at about age 9 or 10, and reach adult patterns at about 13 to 14 years.
- Menarche (the beginning of menstrual periods) typically occurs about 2 years after early breast and pubic hair appear. It may occur as early as age 9, or as late as age 16. The average age of menstruation in the United States is about 12 years.
- Girls growth spurt peaks around age 11.5 and slows around age 16.
Boys:
- Boys may begin to notice that their testicles and scrotum grow as early as age 9. Soon, the penis begins to lengthen. By age 17 or 18, their genitals are usually at their adult size and shape.
- Pubic hair growth -- as well as armpit, leg, chest, and facial hair -- begins in boys at about age 12, and reaches adult patterns at about 17 to 18 years.
- Boys do not start puberty with a sudden incident, like the beginning of menstrual periods in girls. Having regular nocturnal emissions (wet dreams) marks the beginning of puberty in boys. Wet dreams typically start between ages 13 and 17, with the average at about 14.5 years.
- Boys' voices change at the same time as the penis grows. Nocturnal emissions occur with the peak of the height spurt.
- Boys growth spurt peaks around age 13.5 and slows around age 18.
http://www.nlm.nih.gov/medlineplus/ency/article/002003.htm
