Fight and Play, fight and play?

My 5 month and 7 month old kitten play and then my 5 month (5 pounds) whines and cries, then he backs off for a minute and then attacks again. Even once he does give him a break, the 5 month old will attack him! Okay, why would he be pursuing a battle he is going to lose? It looks like playing until the younger one whines, growls and hisses.

For the moment, I have restricted their time together only during feeding.

Sounds like playing to me. In rough play, there are a few growls and hisses.

I wouldn't restrict them. It sounds like normal(ish!) play to me.

If the hissing and growling were at the start not the end, I be concerned. The little one is obviously enjoying himself if he's going back for more

Sounds normal to me as well. Unless theres blood being shed i wouldn't worry. Like Satai said the youngest one must like it to go back for more.

Their both kittens and really just doing what kittens do