Yes, nipple piercings are the same size no matter the size of a girl's boobs. I'm 18, 38DD, and I had mine done about a month ago. They will be the same whether done on an A cup or a DDD cup, and so on. However, since you're not of legal age (18) yet, you will need to go with a parent, sibling, guardian, etc. of age 18 or older, unless doing it on your own at home, which I personally do not recommend as it is much more dangerous than getting it done professionally.