Debate continues on the exact age male dogs should be neutered. Most veterinarians agree that the procedure is best completed while a dog is still a puppy.
The best age for neutering a dog depends largely on the breed and size, but neutering as young as the breed allows can prevent hormonally motivated habits like urine-marking and mounting from becoming part of your dog's routine. Neutering during puppyhood doesn't just help behaviorally -- puppies physically recover from the procedure more easily than older dogs. Some dogs may be neutered as young as 6 weeks old, while others may need be between the ages of 2 months and 6 months. Generally, larger breeds are ready by the time they are 8 weeks old, and smaller breeds may need more time until they are at an appropriate weight.