At present, the development is generally early. If breast development occurs after the age of 9, that is, a lump with small papules appears on the breast, it is normal, and it belongs to precocious puberty before the age of 8, but it is also true and false. Breast development is the standard of adolescence. If menstruation comes, it means that it is mature.

There is a standard age for development: from 8 years old to 12 years old, normal development begins.

Experts say that girls' puberty sexual development begins with breast development, and the arrival of menarche marks the maturity and end of adolescence. This development period usually lasts for two or three years, and the average age of breast development is 10~ 12 years old.

There is a normal range of adolescent sexual development of girls. According to domestic surveys, most girls in big cities begin to develop at the age of 9 years and two months. Generally speaking, the average age of female students in China is around 10.

Generally speaking, breast development is normal from the age of 8 to 12. If it is earlier than 8 years old, it is medically judged as precocious puberty, and later than 13 years old, it is called precocious puberty.

In addition, some children who develop after 12 years old have abnormal conditions, so it is more appropriate to advance the age of late development to 12 years old.

The development is generally advanced: it is related to the improvement of living standards, environmental pollution, media influence and overnutrition.

Experts said that in the early years, most girls in China began to develop in the second day of the first grade, but now, many girls in the fifth and sixth grades and the eleventh and twelfth years of primary school have begun to develop, and their development age is generally advanced.