that's a hard one, since a lot of people wait til their 20's or 30's to marry...but you also don't want to end up being like the kids in the UK, 15 and 13 and already had a baby.
i think its more or less up to the female in the relationship.
because of course 90% of guys would screw on every date XD
i dunno, i guess if you and your partner (well, not you, but you know what i mean) feel like you have a good relationship going, and both willing...why not?
edit, in short...its up to the girl.