Although each adolescent develops at his or her own pace, sometimes influenced by the age at which the parents went through adolescence, the rough estimates are as follows. For boys, their voice begins to change any time between the ages of 10 ½ and 18 years; pubic hair starts to grow between the ages of 11 and 14 years; between 12 and 17 years old, they go through a growth spurt and their body shape changes from child-like to adult; and facial and underarm hair begin to appear between the ages of 13 and 18 years.
For girls, adolescence usually starts approximately two years earlier, with growth of pubic hair beginning any time between the ages of eight and 14 years; growth spurt between nine and a half to 14 ½ years; the first menstrual period occurs between 10 and 16 years; underarm hair first appears any time between the ages of 10 ½ and 16 ½; between 11 ½ and 15 ½ the body shape starts to change; and from 12 ½ to 16 ½ the breast size first reaches adult proportions.
A growth spurt can cause your teen to suddenly shoot up four inches (10.2 cm) or more in one year, and his or her weight increases due to height, more muscle mass (in boys) and body fat (in girls). According to the Centers for Disease Control, almost two-thirds (62 percent) of teenage girls report that they're trying to lose weight, and one to three percent end up developing an eating disorder, such as anorexia or bulimia. Oil and sweat glands are more active in the years of adolescence, resulting in acne and the teen's preoccupation with his or her looks. During adolescence, your teens' brain is still developing, and although they are capable of advanced thinking and abstract thinking, they still exhibit impulsive behavior and black-and-white thinking.