I got my first tattoo at 16, next about 6 months later, next at 17 and third at 18. I was out on my own already so I didn't have anyone to answer to and wanted them. I don't regret any of them, and thought it through, but I wouldn't let my kid follow in my footsteps. I got my ears gunned at 12, and started stretching at 15 and am at 1g now. Im almost 20, so my stretching has been a slow process.
If my son wants to start getting piercings he'll have to wait until hes 15+ for anything other than his ears. It will all have to be discussed and based on other things like attitude, grades, cleanlines, respect, etc. Tattoos I'd let him get one at 17 depending on the same circumstances, and how mature I thought he was and what it was that he wanted.
I know a lot of kids in my school that wnt through a skinhead phase. They all hung out together and they usually changed their fads quite often. They now all have iron crosses and the likes on their chests/arms/legs that they will be embarrassed about until they cover them up.
I know a lumberjack.