Neutering him will actually help - and is better for his health in the long run. Sheesh, your instructor was off base - hitting the dog with a newspaper isn't going to do anything to curb agression! You need to either find a better trainer, or do some serious work with your dog - this isn't impossible, but you'll have to be completely consistent, given he's already 5, so has to "unlearn" the bad behavior first.

After scheduling his neutering, start working with him on a leash, and whenever you see another dog approach, redirect his attention to YOU instead of the other dog. Simple commands like "Sit" and "stay" will give him something to do to focus on you, instead of the other dog, and reinforce that you are the alpha.