since he is still a puppy, i wouldn't worry about it too much. i would make sure though, just like ANY pup, to socialize him very well. puppies are still exploring and seeing what they can or can't get by with, and you should remember that when they're in their litter they do bark and growl a lot at each other! it's normal, they're just trying to play. not doing it is just something they learn from good socialization and being around other dogs, obedience classes are GREAT for this, because on first level classes most are puppies and usually nobody will make mean comments. even my akita (who weighs 135lbs) still does this when he gets too exited. just keep an eye out for signs that it is turning into aggression, and keep being a great momma!