Yeah, it's definitely not an easy situation you're in. It's great that you've had that conversation with him and of course not so great that he can't really define what "ready" is. Unfortunately pressing that issue is not really going to solve anything though and would most likely end up slowing the process in the long run. I know that sucks and isn't the ideal situation but sometimes it is what it is.

I think that giving him some space in the meantime and putting the whole issue on the backburner might be the best bet for now. Obviously your feelings on the matter are just as important as his so absolutely don't be a doormat, but at this point you've made your case and he has made his. The issue and feelings towards it are clearly stated and time will need to be taken to work it out. He's stressed at work and hopefully removing this additional factor of "stress" will help him clear his mind a bit. As you said you're even willing to wait 5 years so at least for now, wait it out and continue as normal. From what I gather he absolutely does want to and plans to marry you so there's no worry there. It's just a timing thing.

And yeah, marriage is beautiful. It's awesome to be able to show and prove to people that this person is literally the only person you plan to spend the entirety of your life with. I guess in the meantime the best way to go about it is focus on the idea behind those feelings towards him and how you DO feel that way towards him and he DOES feel that way towards you. Society can go fuck themselves for now... those rooftops will be there today, tomorrow, and 5 years from now. Hopefully in 4 or 5 years they'll be even taller too, not to mention there'll probably be an additional billion people that you can announce it to!