A male dog should be bred once he has reached his sexual maturity, which happens between 12 to 15 months of age, as stated by the American Kennel Club. Male dogs will often be able to produce offspring once they are 6 months old, but it is not recommended to breed them at this time.
In fact, the American Kennel Club has put strict rules into place so that breeders will be less likely to try to breed male dogs and female dogs before they are ready to be bred. The rule is that male dogs must be at least 7 months old and cannot be more than 12 years old when the mating occurs. Female dogs must be at least 8 months old.