• Puberty may begin as early as age 9 and continue until age 16.
• At puberty, the testes start to produce testosterone.
• Testosterone causes reproductive organs to mature, muscle and bone to grow, facial and pubic hair to appear, and the voice to deepen.

Puberty is the stage during which people reach full reproductive ability and develop the adult features of their gender. In boys, puberty usually occurs between the ages of 10 and 14 years. However, it is not unusual for puberty to begin as early as age 9 or to continue until age 16.

The hypothalamus and pituitary gland, which are in the brain, initiate puberty. The hypothalamus secretes luteinizing hormone-releasing hormone, which stimulates the pituitary to secrete luteinizing hormone and follicle-stimulating hormone. Luteinizing hormone causes the testes to produce testosterone. Follicle-stimulating hormone (plus testosterone) causes the testes to produce sperm. Testosterone is responsible for the development of secondary sex characteristics, features that stimulate male development (including characteristics that are not part of the reproductive system, such as facial hair growth and voice change).

In boys, the first signs of puberty are enlargement of the scrotum and testes, followed by lengthening of the penis. Internally, the seminal vesicles and prostate gland enlarge. Next, pubic hair appears. Hair grows on the face and in the underarms about 2 years after it appears in the pubic area. Ejaculation may begin in mid-adolescence (around age 12½ to 14 years), about 1 year after the penis begins to lengthen. Fertility, however, is not attained until later in adolescence. Breast enlargement (gynecomastia) on one side or both may occur among young adolescent boys and usually disappears within a year.

Milestones in Sexual Development During puberty, sexual development occurs in a set sequence. However, when the changes begin and how quickly they occur vary from person to person. For boys, puberty begins at age 9½ to 10½ years and lasts about 3 years. The chart shows a typical sequence and normal range of development for the milestones of sexual development.

Last full review/revision February 2013 by Irvin H. Hirsch, MD