I honestly don't know, I adopted Vegas when he was 4 months old and he already had been neutered. He is the first dog I have owned in about 10 years and I have had male n. dogs before but I just can't remember at what age. I am sure you will get the right answers, to me 6 months sounds old enough, especially since Vegas already was at 4. Maybe he was to young and that is why he can still go through spells of humping??? hhmmm???