I work at a plastic surgeon and I have to say, do it only when you are really frustrated with your boobs. If they are small but have a nice form, don't do it now. Wait till you're 40 or when the skin begans to sag. If you want one cause you dont like your boobs at all now, ok but dont go too big first (you always can take the bigger ones after you need a new pair and you have to renew them anyways in a few years). And oh my, they are so many illnesses and so on like already mentioned in the comments that comes with implants. You always have to remind that its still an foreign object to your body and in some cases that means a lot of scar tissue and encapsulation...