I am 19 years old and I would like to have a breast reconstruction. When will be the best age to have this kind of surgery?

Breast surgery. The majority if the issues I see with patient who are your age is a difference in size and shape comparing side to side. These issues should be evaluated by a board certified plastic surgeon to rule out polands syndrome. If this doesn't exist then majority if these asymmetries can be treated either though the use of implants or your own tissue such as fat grafting depending on the size difference.
Why? Why do you need a reconstruction at 19? Did something happen to a breast? Both of them? An injury? Or did they not grow as expected? I would go meet with a plastic surgeon experienced in breast reconstruction and breast enhancement to learn about your options. Good luck!
Depends. Depends on why you want or need the reconstruction. If you have a congenital breast deformity (ie polands/amastia) this type of surgery is usually staged and can be started at a earlier age. Plastic surgeons can start a temporary reconstruction while waiting for full breast development in the normal side. If you have a cosmetic issue (tubular)- you may have to wait until you are 22. See a ps!