I also have a dog aggressive APBT, but he is only aggressive to dogs outside of our pack. He’s been neutered since the day we got him at 3months old, but he still developed aggression issues around the age of 3yrs old. I’m currently looking for a trainer in my area to help me break him of this aggression because I just want him to be able to feel calm around other dogs and now so defensive and tense. He is perfectly fine with our toy poodle, Max, running the house hold, and he grew up with a border collie also, who was his best friend & we NEVER have problems with him and our other dogs. But, I don’t think neutering your dog is going to 100% fix his aggression. You’ll probably have to either get a trainer, or dedicate to training him yourself.