Any Advice?

Pretty much what everyone else said.

Don't try and rush into things. She's still in highschool, man. Girls have no idea what they want at that age. If anything, wait till she graduates and if you both still think it's a good idea to get an apartment together, go for it. See how you like living with her.

Quoted for truth:

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.