Hello & Welcome. An 11 year old can be bred however their sperm counts are a lot lower than a younger dog. I would have him checked by a Vet first as the sperm can have physical deformities which can cause birth defects in the puppies. I would have a full physical examination, blood panel, sperm count & motility on them done before I would breed a dog that age, then I would only breed the dog if he was s stellar example of the breed and had something to offer to the puppies, not just because. The oldest I have bred a dog is 7 years old. As they can have problems with their prostates & can get Sertoli Cell Tumors from not being neutered, I chose not to take that risk.