Q. How do I tell how old a pup is?
DAVID ELBEZE, DVM, MRCVS
A. It's not always easy but the things you can tell is if he is over 6 weeks and 4 weeks (molars grow at 6 weeks and canines at 4 weeks). other than that it's just an educated guess.
A. Open his mouth and look for teeth. Puppy teeth begin to erupt around 5 weeks of age. By 8 weeks, they are erupted and in place. In another 8 weeks, they should begin to fall out as the adult teeth begin to erupt. Dogs age at different rates, so it can be tricky. Your vet can give you the best estimate after a complete physical exam if you don't know your pup's whelp date.