My two cents,
In the organization or outside of the organization, our abilities diminish as we age. Even if our skills remain sharp, we should allow younger ones to take positions of responsibility so they can train and be able to handle the job on their own.
What happened to your brother is a fact of life in any sphere of the human experience. We are born, we mature, we age into decrepitude, we die. We should accept this cycle and happily train and pass the responsibility to the younger ones. Your brother has a selfish, rather narrow-minded view of his role in the big picture.