Girls’ breasts develop around the age of 9. It is specifically related to the dietary structure, genetic factors, weight condition and so on. If your breasts do not start to develop after the age of 15, it is recommended that you consult a doctor in time to find out the cause of the problem and then treat it actively. Girls’ breast development is divided into 5 stages. The earliest stage of breast development is around the age of 9, when the symptoms of inverted or concave nipples appear. With the age of 10 years old, the diameter of the nipple and areola will gradually increase, and the areola will also protrude to the outside of the breast, and at this time, you can touch the protruding areola. At the age of 11, the average diameter of the breasts reaches about 4 mm, and the diameter of the areola gradually increases, and the breasts begin to protrude and are not confined to the inside of the areola. 12 years of age, the nipple, areola, and breast will further increase in size, and at this time, the nipple and the areola will protrude, and the breast shows a clear line of demarcation. At around 15 years of age, the diameter of the nipple is 7 millimeters or more, marking the maturity of the breast. If a girl’s breasts have not started to develop after she is over 15 years old, it is clinically called late development. It is necessary to consult a doctor in time to identify the cause and then treat it actively under the doctor’s guidance. Usually when the breasts start to develop, it is recommended to wear loose, comfortable, pure cotton underwear. Usually also pay attention to breast hygiene, it is recommended to eat more fresh vegetables and fruits.