In my experience, most people do not go to jail for this, especially between family members even when police do get involved.
People in this thread that don't understand why one would press charges are acting like it is always a life-ruining situation. It simply isn't, though it could be if it was serious enough to go into a felony charge, which this isn't likely to go there.
I do not believe this warranted pressing charges. I personally I would of fought back and I am very intrigued why OP would intentionally not fight back so he can claim it was assault over defending himself. If he chose not to fight back to deescalate, then I would give him some props, though I still don't agree with it. This stuff can indeed be talked about later with the brother assuming said brother is willing to.
I do not believe in that a family member should get some privilege pass on their actions unless and only unless it was a one time thing in their history. Too many crimes get swept under the rug and covered up for simply because "family". It is illogical to me lol.
If any injuries, fractures and broken/shifted teeth are the most common and you wouldn't always notice fractures. Do fractures count?
It is because they are that old that people believe it is serious and I agree with them.
At that age you should fully understand the consequences of your actions, whether it was planned or in the heat of passion. Also it doesn't take much for one to get serious injuries, unless you think he was holding his punches, he could of easily fractured OP's face or broken his nose.
I am not seeing good arguments from those saying "its just brothers being brothers" though I do agree that pressing charges is not necessary.