I have a small sized puppy that just turned 5 months old and my uncle has a slightly younger dog of about the same size. Every now and then my uncle brings his dog over to play with mine. Their dog is wild when around our dog and he jumps all over and nips at him. Sometimes he will bite and rip* at his ears, tail, or leg. Sometimes my dog will whine (but not often). My dog is calmer and tends to back off then their dog approches it. It also nips back in self defense (in my opinion). I have talked to a friend of mine and she says that an untrained puppy will play like that, but should be trained to play more gentler. She said that hypothetically if a small dog plays like that with another bigger dog, then the bigger dog will attack it. I brought that point up to my parents and uncle numerous times but refuses to consider that and says that puppies are supposed to play like that.
*by rip I mean to grab onto and jerk its head left and right (usualy for a brief period of time)
My question is, are dogs supposed to play like what I described? or are they supposed to play more gentler?