Stomper was neutered at 4 months exactly. He was "ready" for it (matured early) so they said it was not a problem. From what I understand, many dog rescues neuter puppies at 8 weeks old. If the vet says it is safe, it should be fine. Stomper is not little, but he had no problems. Within hours of taking him home, he was back to himself (even with the cone on his head!). Really! In two hours, we feed him (we were told not to but he was fine) and back to his playful self. He is now 6 months old and had no problems. The sooner the better if he is not too small. Less aggressive and less leg lifting!!! Keep us updated.