i think that 18 is not to young if you are happy and can support your child :)
I think that depends on who you talk to. I personally find 18 to be too young. COULD you live together? It's not a matter that you in theory could, it's a matter of if you could handle it. Things change when a couple move in together, and they change even more when you add a baby in the mix. Can you survive on one budget? Do you intend to work after the child born and if so, who will watch that baby? Daycare is FAR from cheap. My family asked for 20 a day to watch my daughter, which adds up to 400 a month. Others will charge by the hour which amounts to THOUSANDS of dollars a month. Do you have your own car? Insurance? Do you buy your own food, do you pay bills? Do you buy all your clothes?
Having children isn't some fleeting thing. How do you know this is the person you're going to be with. Do you intend to be married? What if he walks out on you----and please don't say he won't because you don't know that. I've watched a very great number of couples fall apart because the strain is too much.