What age can you breed a pit bull male?

Technically you could breed a male dog starting at about 9 months of age. However, this is a very bad idea - the dog has not finished growing yet and you don't know if he has bad conformation or traits yet either.

Ideally you wouldn't breed a dog until he is at least 3 years old. This allows the dog to grow into his full frame and muscle development and allows you to see if there are any subtle conformation or behavioral problems that would make him unsuitable for breeding.

Also, you may want to ask why you are breeding your dog in the first place. There are thousands of dogs that are euthanized every year because they were unwanted or abandoned. Breeding your dog will only add to the pet overpopulation problem, unless you are being very careful about what you are breeding, how many puppies there are and who you are selling them to. Pit bulls in particular tend to end up in pounds and shelters because there is a perception that they are dangerous.