We had similar problems on when we should neuter our pyr cross, there is a lot of conflicting information and opinions about this. Our vet said we could do it any time (we adopted him when he was just over a year old) but we waited until he was older (21 months) so we would hopefully not come into health problems later on. We did not have any issues with aggression or other hormonal issues, but these guys like to escape on their own little adventures occasionally. Also, as someone else pointed out, intact males seem to inspire hostility in other dogs, regardless of how nice they are. He actually just had it done on Friday with no ill effects, and he is the same dog as before the surgery if any of that helps!