I moved in with my bf at 20 (he's 8 years older than me) into his place. we bought our first place together this year - me 22, him 30.
to be honest though, what i did is academic; if you don't feel ready, then don't do it. i would also say that perhaps you might want to think about renting first; buying together brings with it lots of financial ties that are difficult to get to get out of if it doesn't work out. i found living with my bf in his place first (contributing to the bills but not getting involved in the mortgge - paying rent i guess) a good way to figure out whether we could live together.
relationships take on a different dimension when you live with someone; you have to deal with their bad habits, accept that they're going to hear you go to the bathroom and other non-glamouros things like that. if you rent together before you buy, if it doesn't work out it's a lot easier to get out of the arrangement.