personally, if I were him I'd run a mile after reading this. this is precisely why guys are scared off by marriage - your question makes it seem like his life is flashing before his eyes.
you're far too young to get married, you'll both change so much before you're even 30, why the hurry to "just play that role" be patient and let him see that he wants it too, in his own time.
"he plans on marrying me but I don't feel like waiting around for it to happen. How do I get him to pop the question sooner", you can't force him to do it any sooner - unless you ask him yourself, so why haven't YOU proposed to him yet?
Seriously there is no rush to get married these days, even if you were pregnant. Wouldn't you rather use the wedding money to have a fabulous cruise/holiday instead and really cement your love, maybe planning that would keep you occupied for a while? Just a suggestion, also there's nothing wrong with being boyfriend/girlfriend - a lot of relationships turn sour after the wedding - something changes.
you have your whole lives ahead of you, if you're that sure of each other then there is no rush at all.