I'm also your boyfriends age, and to me the 22 year olds I know are still so young - and I mean very mature ones. The brain keeps developing till 25. I really believe that to be true, looking back: at 22 I worked, travelled, lived independently, pursued career goals. I also had some relationships with men in their late 30s. Looking back, I absolutely put up with behaviour/put on a pedestal men who I would engage with totally differently now. It didn't do me any harm, but I wouldn't be happy to be married to any of them now!
The most 'successful' age gap relationships I know, with a man similar number of years older than you, the man waited to have children until the woman was at a suitable point in her career, which translated to 30. If I were you, I'd wait till you were 25 at least to marry.
The majority of relationships I know with that age gap, all I can say is I strongly feel the younger party (its so far always been a woman) wouldn't have got together with the older one if they were closer in age, say five years. As in, the smart together 22 year old who I met when she dated my 36 year old room mate, who thought he was so sophisticated because he liked wine and foreign films and was so much more well read compared to her contemporaries, I would 100% swear if she had got to 36 would have given him short shrift for his inability to use a hoover and general emotional immaturity.
If you think you could marry and have children with him, then that will still be the case in a few years: if he's not prepared to wait that long then he's not the one for you.