Age estimation

When Kerry was rescued by the RSPCA they estimated her age at about 3, so they made up a date of birth to match.
Are there any objective ways of being more accurate?
We've been wondering about the increasing greyness to her cheeks but humans can go grey at almost any age.

Not really I don't think, what does your vet say? Yes us humans can grey early, my son is 20 and has had grey hairs since he was 17

Teeth are a tell tale sign but will never be able to narrow it that much, they can grey at any age tbh and Moo just has a gotcha day and is always 3ish 4ish...

they tend to age dogs with their body condition and their teeth. Thats how we've got an estimated age for Chance of 4

what colour is she? my tessa is a rescue and around 5 years old she is black/brindle and white and has had a grey chin and flecks of grey on her cheeks since we had her in april 2012 when she was around 3. i had 2 litter sisters in the early 90s from pups and one of them was black/brindle and white and she went grey quite young.