It depends.
I'm 21, and my girlfriend is 17...
It seems perfectly normal to us.
Just like Ronstang said, her parents are actually pretty thankful she found me.. rather than some of the other lovely individuals that live around her...
Happydaddy - Yeah, and you damn dads need to backoff a little.

Her dad is having some problems watching his little girl grow up, so to speak. He doesen't dislike me.. He just won't let me stay the night there. lol.. even though we get to sleep with eachother down here at her moms. lol.... It's pretty funny, actually.