Young marriage

My boyfriend & I have known each other since middle school. He recently graduated highs hook & joined the army. He's met my family & gone through that whole ordeal & is now talking about marriage. As much as I would love to marry this man I don't know what's holding me back. He's 20 years old & stationed far away from both of our families. I'm turning 18 in December & going to visit him this summer. Has anyone else gone through this? I know he's the man I want to marry & I know we're young but why do I have this "giddy" feeling whenever I think about it?