There is some confusion as to how old my parents dog was when they got him (rescue dog) They thought he was 10 wks, but when he went ot he vet for his final puppy shots, which would have been at 4 mos, the vet said he had teeth he shouldn't get til he was 6 mos. So, long story short (too late!) he was neutured at either, since was neutered when they adopted him he was either 9wks or almost 3 mos. either way, they 3 mos later there have been no negative ramifications. As long as the dog is healthly, 4 mos should be fine, but it would be up to your vet. Ours won't do it before they are 6 mos.