The Australian Shepherd showlines pritty much no longer carry the gene for premature greying. It is beleived to be a dominant trait that is easily bred out. And since dogs with richer color tend to win more, they are the ones who pass on their genes more. so I would say 85% of aussies do not have this gene.
Rufus is a 2 year lab/wolfhound? mix. He has a few gray hairs on his muzzle, under his eyes and a few on his back near the base of his tail. I actually think he is less gray since I brought him home from the shelter... hmm
Belle is 9 and only has a few grey hairs on her chin. Shadow's 10 and has been grey & white since he was about 1 1/2, he was black & white as a puppy. Not sure if it counts as premature greying though...it might had just been a color change from pup to adult?? not sure.
Jade is 1 year 5 months and she already has the front of her muzzle full of grey/white hairs. To people that see her here at the house... she already looks old because of it.
Why does it happen? Danes age quicker... and well she's black... so you notice it way more than with Callahan. By the way she's going... I wouldnt be surprised if she's fully white on her face by the end of next year.
It's hard for me to say. Marge doesn't have the typical white hairs starting around the nose/eyes, but she DOES have a few spread throughout her body that I haven't noticed before. One of her brothers is prematurely gray, though.