It varies. My male is 6 and is just barely starting to go grey. He's got a little grey soul patch on his chin and a few grey hairs here and there on his face.
Thanks for sharing the picture of Honey. She's beautiful and has the sweetest face! I'm sure stress could play a role but my guess is that with some dogs, it's mostly genetics.Honey will be 5 this month and her face is really gray. She's been getting gray for at least two years. She is very afraid of thunderstorms and other loud noises. I often wonder if she is so stressed that it turned her gray earlier. (Just like people.)
I will say Jasmine acts younger, too. It doesn't last as long as Danny's burst of energy, but she hangs with the boys. Jasper wears out before she does.My Bentley definitely started graying around the muzzle when he was six. He is going on nine now, but I think he acts younger than he did several years ago.