What are the federal laws for underage nipple and genital piercings?

It depends on what the Federal government considers "exotic" for your country. To purchase sexually explicit material there is an age limit, this is generally where the Government has define this as being material suitable for "adult consumption" only. The best rule of thumb is to assume that any "exotic" piercings (this includes female nipples) requires the person requesting the piercing to be of legal age of *majority ( *legally be an adult in the eyes of the law).

Parental consent doesn't matter and has no legal bearing when talking about "exotic" piercings (this means even if your folks say it's fine and they will sign for you, the studio doing the piercing may not legally be allowed to perform the piercings due to local or state or provincial morality laws and city bylaws. So doing your local research is important, contact your local city hall bylaws office, as well as checking with your local state or provincial health protection and inspection office.

If you are still in the dark with no answers locally you could always contact your municipal or city police and your provincial or federal police in regards to offences against minors. There are less than reputable studiOS that will do almost anything for cash, so you need to know who you are dealing with is on the up and up, keep in mind if they are willing to bend laws to do something for you, chances are good there is more things they are not doing that they should be (sterilization, disinfection, discarding used needles etc.)