The thing is, grey hair might age you (but - why does it age women so much more than men? Does it, actually? Or do we just perceive it to, because we're conditioned to see older women with dyed hair?).
It also might not age you. Dyed hair might be the aging factor. Everyone is different.
As someone who dyes their hair at 41, with considerable grey coming through at my front parting and temples, this is something I have to start thinking about.
Personally, I think it is entirely possible to look great at any decade, and at any age (although naturally, it takes effort). I don't think you have to look 10 or even 5 years younger in order to look good.
I would far rather look elegant, sharp, attractive, relevant, stylish, whatever, than young, per se. Yes, it's always nice when people are surprised to find out one's age, but there come a point (perhaps not yet for me) when you do start having to making adjustments to your look.
I do agree with others who say weight and clothes choices are almost certainly far more aging than hair color.
Thanks to this thread, I'm beginning to think that all things being equal, it's dyed hair that falls short of the mark, long-term.