With how nonsensical things are in the movies, nevermind the comics, I think it'd be a non-issue (and really fun) if it's never addressed that once he dons the armor, he just never ages and it's never explained why. He just shows up at different time periods and remains exactly the same.
Doom technically is more magic oriented. His armor was initially (and remains) enchanted and he's only ever added to that. Doom's whole thing was that he's so smart that he formulized magic into a new scientific principle, like Newton and calculus, except no one understands Doom's work besides him. It's been stated numerous times that he would be the Sorcerer Supreme if he wasn't such a jerk.
I think it would also be a huge dishonor to not just translate his armor literally from the comics and forgo the "seams and plates" look every single Marvel hero has in the movies. His armor was handmade by craftsmen-wizard-monks in the remote mountains of Latveria specifically for Doom. It should look traditional more than "space-y." Given Doom's nature, as well, he'd make additions to the suit over time, but it should be kept traditional as a point of Latverian pride.