Why are you asking if it's ever a good idea to get married young? That isn't what you want to know. You want to know if there is some magic trick you can do to get your GF back, or travel back in time to a better place in the relationship. If you're considering marriage with this girl forget about it. It's too late for that, and it would be a bad idea to marry her anyway.
We can talk about why young marriages last, or don't last, and what's needed to sustain a marriage etc, but that is not what you need to hear. She broke up with you and it doesn't matter why. It especially doesn't matter what she SAYS about it. The relationship is OVER, forever. You don't want to be "friends" and you don't want to keep in touch. You need to do what's best for you, and that means cutting her out of your life and moving past it.
We have ALL been there, and I know it is much easier said than done, but this is a process you need to go through. Over time, and it could take a long time, she will be a distant memory. You will take so much away from this experience, and be a stronger person for sticking through the pain instead of prolonging your misery trying to get back with her. Commit to NC, and that includes FB stalking, twitter stalking, etc. You need to delete her from all of that stuff. If she asks you why you're deleting her, you don't need to answer. But if you want to answer, don't engage in a long conversation just tell her it's for the best. She WILL reach out to you for attention, but you have already made the decision that you're not going to give her any more because it is in YOUR best interest.
She is NOT the perfect girl you thought, because that concept isn't real. She will grow into a completely different person, and so will you. When you feel like you NEED a girl in your life you aren't in a good position, and it will only lead to pain. I found this site probably two years ago under the same conditions as you, and I am so much smarter and happier than I was. I know it's a hard process, and I was in really bad shape for months, but honestly, that pain was necessary to become better. A lot of guys in your position won't ever learn - they'll do something dumb like propose to a girl.
