Seems, he is of Eastern line like my dog, they are larger in size, straighter back legs, they are bulky, with prominent muscles and have massive paws. Was it a Czech breeder? Or DDR? If that is so - you wouldn't have any problems in training him whatsoever, he would never run away from you for any reason on earth, these dogs are silent dogs and it should be easy to socialize him. Your problem is exercising him, they are purely working dogs and without a daily intellectual and physical heavy load he might fall into depression or become agressive. A very beautiful boy, and his facial mask is impressive! But, it is difficult to judge him before he's 1 year old.