If I were to breed,
1. I would try to aim for the first litter to be around two years of age
2. I would not attempt a first breeding after 4 years of age
3. I would not breed a female over 6 years of age and would have her spayed to avoid pyrometra
1. I would not breed a male before he is old enough to have earned the right - 2 years minmum.
2. A seasoned experienced male would be fine as long as mounting and mating is not uncomfortable for him and he is in good shape. I would love to see healthy males at 15 years of age still mating as hopefully long life can be passed to the pups.
This is just my opinion as a dog owner not a seasoned breeder.