IMO it depends on sexual history.
If she's the 'virginal' type, then don't. A girls future sex life often follows her first experiences. (she will most likely continue to go after the same sorts of guys and the same sorts of relationships)
That's a ton of pressure. (if you have a conscience)
If she's already been with a half a dozen guys and has a casual attitude towards sex then she's 'mature' enough already and you're personally less responsible/influencial over her emotional health.
