From what I've heard, this will only happen once they're mature (2+yrs old). Some dogs may never be protective. My last GSD was 4 yrs old when I rescued him and he never really showed any signs of being 'protective'. He was serious and aloof, but wouldn't go out of his way to deter anyone if that's what you mean. My current one year old is way too silly to be protective. If you have a happy, confident 5month old then that is a good thing! Fear is not really what you want in a young (or any) dog. Let him be a puppy, he will develop into whatever dog he will become in time.