This age depends on personal circumstances. You can ask at Grammy in Hangzhou. Bad living habits and unhealthy living habits will also harm your chest development, for example; Wearing underwear that doesn't fit the chest shape will kill the original beautiful chest shape. Too tight cups will leave no room for breast development. Too loose underwear will turn the chest into fat and will not concentrate. Even a layer of fat will appear under the chest, but the chest is still very small. Solution: Keep a good sitting position, standing position and sleeping position, don't indulge yourself, and don't be too good to yourself. Wearing the right bra is king.