Is there anything giving a general idea of behaviors to expect at different ages for the GSD? Or is each dog too different to generalize guidelines like that? The only reason I ask is because I have always walked Gunner around the town I live in - on side streets, neighborhoods, and the main drag. He has always been fine walking on the main road and the cars and such have never bothered him. Recently he has been startling at the diesel trucks and motorcycles passing by and has even tried to go after the vehicles by jumping up at them and trying to run after them. He is now about 13 1/2 months old. When he does this I get him settled in to a sit and then treat him for his nice, calm behavior. Should I be reacting differently when he does this?