I don't see anything wrong with tattoos or piercings as well, however, tattoos at least, are pretty darn permanent (or at least very hard to remove). Until a certain age or maturity level kids aren't always able to see far enough in to the future to a time they might not want to have...say... taz on their forearm, so it's up to the parents to help make those choices. What that age is exactly depends on biology and social maturity.