Would it be hard to RP as a bum or an old man in this game? I have a feeling with everyone calling me the "kid from vault 101" would ruin me enjoying my RP. I was going to do it in NV, but I think I should do a real Fallout 3 playthrough, and I want to play as a bum since I've played as just young dudes before.

You could avoid GNR (Three Dog refers to the PC as a kid a ton), but it'd be tough to play though the main quest while trying to legitimately RP as an old person.