MY four month old bites my pant legs and shoes. I correct him for doing this, but I am not concerned. I think it's just puppy behavior. He is in a traning class and in two weeks will start IPO training. With my first GSD we put the stop to the biting fairly quickly, but I don't think we should do that with this one if he will be learning IPO.
If you don't want him to bite there are ways to stop it. With our first GSD I would put my thump inside his mouth, but pressing on his bottom jaw applying pressure, but not pain. The dog won't bite down and when he started to shake his head, because he didn't like it I would say "NO BITE". This worked really well for our first GSD. I know there are other methods out there too.
Anyway, I don't think it's a sign old aggression on a three month old pup. They are just playing. You can try to redirect him to a toy also. When Kaleb bites my hands I get an antler or a nyla none for him and he'll work on that for a bit.
Riley - 11/05/2012-8/30/2013
He will always be in my heart.