Some of it is his age, he's just a puppy and still learning. When he even nips at you hands, "yelp" and pull your hands up where he cannot get them, and turn your back on him until he calms down. It make take many repetitions, but he will come to realize that when his teeth make contact with you, playtime ends, and so he's stop that behavior. Just make sure everyone in the house understand this, and is consistent. Pups chomp on each other in play all the time, but they ned to learn that's not acceptable with the humans, we don't have fur to help protect ourselves from those sharp teeth!