I entered this thread with a convincing "lol of course grey, that's not even a question", but reading the rules you're making it somewhat hard on me. I mean, being "completely bald" on 60 isn't too bad. I don't think I'd care about it too much by then. And while grey hair can look awesome as fuck, I prefer my current black hair. Being completely grey at 30 would be kinda jarring.
So yeah, keep a head full of hair and go bald at 60. I'd sign for that shit right now. I'm 25 now and it's starting to thin terrifyingly fast.