What developmental changes occur during adolescence?

Explanation: Adolescence is a time for growth spurts and puberty changes. An adolescent may grow several inches in several months followed by a period of very slow growth, then have another growth spurt. Changes with puberty (sexual maturation) may happen gradually or several signs may become visible at the same time. 

Sexual and other physical maturation that happens during puberty is a result of hormonal changes. In boys, it is difficult to know exactly when puberty is coming. There are changes that happen, but they happen gradually and over a period of time, rather than as a single event. While each male adolescent is different, the following are average ages when puberty changes may happen:

Beginning of puberty: 9.5 to 14 years old

First pubertal change: enlargement of the testicles

Penis enlargement: begins approximately 1 year after the testicles begin enlarging

Appearance of pubic hair: 13.5 years old 

Hair under the arms and on the face, voice change, and acne: 15 years old

Girls also experience puberty as a sequence of events, but their pubertal changes usually begin before boys of the same age. Each girl is different and may progress through these changes differently. The following are average ages when puberty changes may happen:

Beginning of puberty: 8 to 13 years

First pubertal change: breast development

Pubic hair development: shortly after breast development

Hair under the arms: 12 years old

Menstrual periods: 10 to 16.5 years old 

In girls, the initial puberty change is the development of breast buds. This is when the breast and nipple elevate. The areola (dark area of skin that surrounds the nipple of the breast) increases in size at this time. The breasts then continue to enlarge. Eventually, the nipples and the areolas will elevate again. They then form another projection on the breasts. At the adult state, only the nipple remains elevated above the rest of the breast tissue.