These are good questions, and easy answers I don't have. I suppose it depends on the breed, but Cali/NZ crosses can live 7 or more years. Some folks will chime in and say they pet lived for 10 years... I don't know.
I've never found any charts that said that Breed X lives 5-9 years... maybe there is one, I just haven't found it yet.
Seems to me, if your vet knows rabbits (big IF) that a teeth/mouth exam could give you a guess.
The only way to know for sure is to know who bred them and if they keep records and tattooed the rabbit. Teeth really can't help as they continue to grow throughout the rabbits life. A vet could guess, but it would be just a guess. I've got a New Zealand White buck that is 7yrs and doing well.
We got her around easter time at the vet. She is around 7 years old, and she LOOKS old. I don't know what kind of breed she is. She's medium size black and white with shorter ears.