I'll add onto what Jonathan said:
1. Wait until this honey-moon phase is over to see if you really can battle the odds
2. Get a little older. You're still growing. I'm not saying there aren't exceptions, but marriage at such an early age is more often than not ill-fated
3. Make sure your girlfriend is ready too. This can't be a one-sided deal.
4. Really think about the meaning of marriage. It's not a game. You will be spending the rest of your life with this person, it'll no longer be 'I', you'll have to make sacrifices and compromises, you'll have to work it out, you have to stay committed, and there's so much more that is probably beyond my scope since I'm not a married person.
