I had a similar problem with a small, intact border collie. My lab mix was fixed at 6 mos and played with a border collie half his size. When the border collie hit about 8 mos, he started to brutalize my dog, he was too small to do any damage, but he clearly wasn't playing. And, after that incident, the border collie wouldn't play with anyone.
I don't think it is only being intact, b/c my dog can play with intact Pit Bulls and Labs with no issues... unless things get too excited, then I have to calm things down before they escalate...
But, I think you might find other playmates ...