The issue with Captain Marvel (which may or may not be that serious, i dunno) is that she's supposed to have the ranking of Colonel in the Airforce.
Now I know nothing about military rankings so i couldn't tell you what any of that signifies, but apparently (or realistically) you don't get that title unless you've been in the game a long time. Meaning if they're trying to be 'accurate' she's likely not going to look like a hot young blonde in her mid 20s. The common playful jab she uses at Steve Rogers in the comics is that she actually 'outranks' Captain America.
Now do they have to make her a veteran colonel as opposed to just a young recruit in the airforce? The general public wouldn't know the difference b/c they don't know the character but it's just one of those things. That's why i think Blunt could work b/c she doesn't look too old nor too young, if they want to go with the colonel route.