Not worrying about the law or parents, I've never known a girl that age who's honestly mature enough to have an intimate (even just emotionally intimate) relationship with a normal 20-something guy. If you want to convince yourself that it's okay, you can, but you'll be wrong... and you'll realize that after you've f***ed up her emotional development for a long time.
Yeah, it is disturbing how good some of the young 'uns look. It's biological - evolution doesn't work as fast as social convention, and we're still designed as a race to reproduce as soon as possible.
