How long has your in game clock gone my longest guy is right aroun 8 months so he wouldn't have aged any reall and as for hair and beard I never really thought about it but I'd assume my guy just trims his beard and gets a haircut every few weeks. I don't thinking making hair grow and adding some sort of up keep system to the game would be worth the effort since I can't see more than a handful of people likening it and everyone else thinking its a stupid chore.
Yep, I personally don't see the point in making it mandatory; optional is fine, but mandatory would make it annoying for anyone who doesn't want the feature. And my clock is about 4 years so he'd have hair down to his back or something

Plus, if we were adding in stuff like ageing, we might as well add stuff like scarring (which could be removed via, say, a doctor or an Auto-Doc).