Children: 7 years old-14 years old.

Juvenile: 13 years old-19 years old.

Children: 18 years old.

Youth: 20 -39 years old.

Middle age: 40 -59 years old.

Old age: over 60 years old.

According to age, China is divided into four age groups, namely, youth group (under 29 years old), middle-aged group (30-39 years old), middle-aged group (40-49 years old) and middle-aged group (over 50 years old).

Fetus, infant 0-0.6, infant 0.6-2, child 3-6, teenager 7- 14, youth 15-35, middle-aged 36-60, and elderly 6 1-, which are generally divided.

Generally speaking, the ancients divided the time like this: childhood is under 12 years old, and over 12 years old is called the age of juvenile total angle. A weak crown at the age of 20 is a youth, and some people think that after 18, it stands for a youth, and it enters middle age, and it is called a mature age. ...

According to developmental psychology, it is divided into: suckling period 0- 1 year-old infant period 1-2-year-old infant period 2-3-year-old preschool period 3-6, 7-1,12-year-old adolescent period1.

Internationally, the population is usually divided into unequal groups according to 0~ 14 years old, 15~64 years old and over 65 years old, which are called juvenile population, mature population and old population respectively. The juvenile population coefficient, mature population coefficient and old population coefficient are calculated based on the total population, and the dependency coefficient is also calculated based on the mature population, that is, the dependency coefficient = (juvenile population+)