I think you have to consider the individual dog. I've had a male who was entire till age 12 with no problems. He ended up being neutered because of prostate trouble. My current two got really out of hand to the point of risk to themselves and others...not aggressive but no recall, would cross roads etcet to get to other dogs. Neutering chilled them down enough to listen and remember their previous excellent behaviour. We wanted to wait till they were 2 to decide but we honestly didn't think we could risk it so they were done at 18 months...end of the day its up to you. "having a pop" can be learned behaviour, neutering will probably not stop it but might help if he no longer feels so "manly protective" around the bitches, you will still need to train though.