Oh, I read it as her being 18, not almost 18.

So, you're talking about having kids with a 17 year old. I would seriously watch out man, she might seem mature but if she's still living with her parents and in school, she's not. Wait until she's 18, get an apartment with her, see how that goes for a while. You can't truly know if you can spend the rest of your life with someone until you live with them. You find out a lot more about a person, spend a lot more time with them, and get annoyed by their bad habits. It's quite a trial for any relationship, but a very necessary one.