
My vet told me that as long as the bitch had finished growing anything from 18 months plus is acceptable, providing of course, all the relevant health checks have been done.
But it sounds like this will be your first litter, so I suggest you forget the December season and concentrate of learning as much as you can BEFORE breeding, get all health checks done and go back to the breeder so they can help you find a suitable stud dog!
Good luck