Generally speaking, plastic surgeons prefer to wait until a patient is 18 years old before performing their surgery. This is a rather arbitrary age, however, there are two reasons for this. First, at age 18, the patient has pretty much reached their full adult physical dimensions. In other words, they aren't going to grow anymore. Breasts may change with weight gain/loss, periods, pregnancies, etc. but at 18 they are now adult breasts. The second reason is that, at 18, we consider patients more mature and better able to handle the mental and emotional aspects of surgery and its consequences. That said, there are exceptions to every rule. This is one of those instances. If your daughter is not overweight and otherwise fits the criteria for a breast reduction then most plastic surgeons will perform her surgery regardless of her age. I would suggest that you schedule an appointment for her to be evaluated by a board-certified plastic surgeon who can examine her and review her options with you.