Bro,i breed dogs. 3 years old is a GOOD age for breeding because the organs are fully developed already. Just make sure that if you plan to breed the dog,you supplement her with the right food and vitamins. Give her enough exercise and deworm her before breeding. It's better if you consult your vet for queries regarding breeding your dog. Ask about the PRO's and the CON's about breeding because im telling you that breeding a good and sound dog is EXPENSIVE. If you plan to breed your dog,have a SMEAR TEST also so that you won't miss the right time she releases her eggs..