The breasts of 17-year-old girls are similar to adult breasts and are already developed, with the nipples and areolas of the areola blending into the round shape of the breasts, and the nipples and areolas protruding forward in the shape of a small ball. Normal breasts begin to develop at the age of 9-14 years, with most developing for an average of 4 years. However, individual differences are large and easily influenced by genetic factors or nutritional status, endocrine hormones, etc. Most of them feel swollen breasts and tingling nipples a week before the first menstruation, which is normal. If the breast development is small at the age of 17, there are factors related to heredity; if the breast development is small and accompanied by abnormal physical development, menstrual secretion disorder, etc., you should visit the hospital in time for sex hormone and chromosome, abdominal ultrasound and other related examinations.