Well. The initial period of tongue swelling is a real pain in the rear, I talked funny for at least two weeks.

I got my tongue pierced at about 19-20 years old. I sized up to an 8 gauge at the largest, that was too big for me, I dropped it back down to a 10. I took it out about when I was 22-23ish because I worked in an office. At 32 I can still put it back in if I wanted to, it's never fully closed up.

Anyway. I never had any problems with tooth chipping. Biting down on it while eating is REALLY uncomfortable (thank goodness for strong teeth).

I noticed that after I took it out I could taste food a lot better. Go figure. I've known quite a few people that have had their tongue pierced and no horror stories. (unlike a lot of horror stories from bellybutton piercings)

All in all, wait until you're 18. If you still want one, know the risks, and if it works for you go for it.