Alerting at the door, barking at strangers and noises, etc, isn't protection. That's a watch dog. My pug does that stuff. He barks, you get up and check it out.
I wouldn't expect any true protective abilities to come out before 2 years or so, depending on the breeding of the dog and how much defensive drive it's got. Some lines mature even later. Most of them simply are not mature enough prior to that. A 10 month old dog that bites someone is most likely doing it out of fear. They figure out that "hey, if I bite the person, they go away and leave me alone". That's not a good thing, because now you have a fear biter, one who realizes that if he uses his teeth he can make a threat that he doesn't want to deal with go away.
We had a 2yr old white GSD at our dog club who was like that. He was all huff and puff, growling, barking, but he'd just assume cheap shot the decoy rather than engage. When the guys who ran the club finally told the handler they were washing the dog out, that he didn't have what the club was looking for, the handler got all mad, and said, I know he can do this, I'll show you. Just to prove it to the handler, the decoy said, fine, I'm so confident that he won't do it, I'll go out in the field with no gear on. The handler sent the dog, the decoy made a threatening move toward the dog, and then chased the dog off the field. Then he took the handler, put him in a headlock and started to scuffle to see what the dog would do. He did nothing.
So- even when mature, not every GSD will "protect". If barking and growling are enough to keep people away, that's all good, but please remember that not every dog will come to your aid if a bad guy is trying to hurt you.
