As long as they're not hideous, pretty much anything is acceptable, really. That being said, there was a game where the MC was a ginger and I thought that was a bit too specific.
Definitely no fat ugly old guy. Hate when they have them, especially the unavoidable ones that are total douchenozzles in Female protag games (blackmail is a tag I filter out.)
Nothing ruins a character model faster than the dialog being completely out of whack. I usually don't like shota characters because they talk like adults. So make the MC an average guy in his late 20s or 30s, since that's what most developers are able to write convincingly.