Abby just turned 3 years today. 4 months ago she started graying on her muzzle and around her eyes. This is my 6th Golden and none grayed or whitened until 10 or 11yrs. Is this a symptom of anything other than just gray hair?

I have a little solid black pom mix and she has had gray around her muzzle since I got her at 1 year of age... everyone keeps telling me she is older because of that... but her teeth and attitude doesn't show that.

I'd generally say "no", but because it's unusual for your experience, it might be worth investigating. Since this doesn't seem like a medical emergency, you might want to see if you can find a golden retriever forum and post there and see if other golden owners have had this happen. Based on what you learn there, it might be worth seeing a vet.

Just as an fyi: black greyhounds are known for graying early. So maybe this golden is darker than the others you have had, so the grey shows more?

That is way too early for a Golden to be graying. I would get her into the vet. Depending on what the vet thinks, some tests might show up something.