My cat plays aggressively with our kitten?

Two days ago, we brought home two new cats from the local shelter. One is 5 months old and is very large for his age( he appears full grown) and the other is 2 months old and very small. The two get along very well but when they start to play, the older one gets very rough with the younger one. It eventually comes to the point where you have to pull the older one away because he's biting and holding onto the younger ones neck or stomach. We think that the older one may have been an only kitten or been taken from his mother too soon and never learned how to play properly. I don't want to punish them for playing but Im worried that the kitten will get hurt. Both are neutered and very friendly. Any suggestions on how to fix the problem and maybe teach the cat how to play nice?