Wow... That is a totally huge step. If you're not ready to be married it's understandable, seeing how you have your life ahead of you. Just tell him to hold off for a little while if you aren't ready, because rushing into things when you're unprepared can ruin it forever. If you're ready to commit but you're scared then talk to him about it and try to fix your problem. This seems like a slightly bad idea because you reallly don't seem ready. And if he asks and you're still not ready, just say that you need some time to think about it or something that would give you a bit more time without saying no, because saying no might hurt him. Good Luck and I hope you boyfriend will hold off.