Age for nipple reduction surgery
Generally, you want to wait till you stop breast-feeding before undergoing nipple reduction surgery since there is a distinct chance of damaging the delicate milk ducts that leads from the deep aspects of the breast to the nipple itself.
Of course, there is a simple nipple reduction which decreases the height of the nipple just by taking the skin around the "neck" of the nipple itself. That will reduce the height of the nipple and therefore will not damage any of the milk ducts. In this case, you could undergo surgery as soon as it is a appropriate.
It is best to wait until you are about 18 or 19 years old before considering any form of cosmetic breast surgery. This is because your breasts are still developing before this time. You may also want to wait until after you've stopped having children and breastfeeding, since your breasts will undergo more changes which can adversely affect the results of previous surgery.
That depends on your specific circumstances. if you are under age 18, your guardian must consent for you for surgery. For most breast surgery, it is advisable to wait until at least puberty has ended, and consider waiting until after you are done having children (for women). However, some circumstances require earlier surgery - if you are having problems with pain, skin irritation, or significant emotional difficulty, for example. It is best to consult with a qualified surgeon to understand your options.