How does this sound for a marriage proposal and is it too soon?

Pump the brakes...you haven't even been together for 6 months & he's not even 21?? I would say that's waaay too soon. It doesn't matter if you've known him for over 3 years - I was friends with my boyfriend & being friends with someone & dating them are completely different. You get to know them on a whole different level. If I were you, I'd wait to finish college. It's fine to discuss the idea of marriage right now, but don't rush it. Make sure he's on the same page as you & just be patient & wait for HIM to do the proposing when he's ready.