I think it's fairly personal as to if you call yourself a greymuzzle or not. Do you feel old or older? Do you feel like you've been in the fandom a long time? If so then sure, call yourself one, but I'm not sure there is (or should be) any fixed definition.
I agree with Loc. I first started drawing furry characters over 30 years ago, but I don't feel
any older other than being a little stiff in a few joints.
At 69 I can probably call most of you furs young pups, but one is as young or old you as you
feel. I see no reason to feel it's childish to have fun and enjoy fantasy stories of anthro animasls
and dragons. I imagine some women still like to fantasize being a princess saved by a knight in
shining armor. Some might say I am in my second childhood, but if that's the case I never left
I have enjoyed reading and seeing anthro animal character stories since I was a little kid.
I think it's sad for people to think they should leave fantasy or dreams to the young, We live to
short a life to give up fun and fantasy. Not to say we shouldn't be responsible, but enjoy your
dreams. As long as they don't hurt others it should be fine in spite of those old stuffed shirts out
there who think we are foolish.
So greymuzzle or not I plan to be a furry as long as I can. Even it's just reading or listening to
stories about it.