German shepherds are not aggressive dogs, they are very protective, but not aggressive. Dogs are not naturally aggressive, either people make them that way, or the breeding was poor, meaning they did not make sure the two dogs they bred had excellent tempermants and that their ansectors did as well. Your shepeherd is only a puppy, he is not fully matured yet, but is showing you part of what his maturity will bring. My best friend has a solid white german shepherd who acts scared at times. She'll bark when you ring the door bell, but when you come in, she'll crouch and run, but come back to greet you while still crouched and tail wagging. You need to make sure to socialize and train your puppy everyday to ensure his well being and attitude towards things. Puppies take alot of time, effort and commitment to train, socialize and care for them. It's a big responsibiliy. But yes, it could also be your size. The puppy was intemmidated. Just like if an elephant charged at me, i'd surely be intemmidated! :) I hope i've helped some!