Difficult
It depends on whether she's just broody or if there are deeper issues there. Frankly at twenty she doesn't need to start to think about it for a while yet - I'd go so far as to say you'd be better off enjoying life for a bit, getting a career and a mortgage etc and then taking the plunge.

However, if - like an ex I posted about a while ago - she's utterly fixated on having babies as a means of distracting her from inner-crappiness - then I'd exercise caution.

Nothing kills a relationship like the threat of an unplanned (by one partner at least) pregnancy.
(Bicycle Repairman "you're also a bit of a wanker", Fri 22 Aug 2008, 14:48, Reply)