[Kris10]

He was very young (TOO young) when you got him. This is how he would play with his litter mates and naturally learn about bite inhibition. This is normal GSD puppy behavior. You will hear from a lot of folks on this forum about how to deal with this-it is pretty common! I still have an issue with my Max being mouthy (although he doesn't bite hard). I have heard that you should try responding with a yelp, as his siblings would have, so he knows he has gone too far with his bite.
Please be patient with him, as your time spent playing with him and training him now will be so rewarding when he matures!