When to neuter. A male dog can be neutered any time after eight weeks of age. A few years ago, most veterinarians advised waiting until puberty hit at about six months, and some still make that recommendation. Talk to your veterinarian about what’s best for your dog.ost dogs are sexually mature by the age of five or six months (the blink of an eye). If your dog’s testicles don’t descend, you still need to have him neutered. These dogs tend to have more testicular tumors than normal dogs.