One day your little brother might be better than you at your own sport. Cheer the loudest anyway.

Being passed by somebody younger in your own event lands as a demotion, and the first feeling is rarely generous. It helps to see what is actually happening: he learned partly from watching you, and none of that gets taken away by a faster time. Nobody else is scoring the two of you against each other. Only you are keeping that table.

So go to his game and be loud on purpose, where he can hear it. Tell him the specific thing he does better than you. It costs you nothing and he will remember it for twenty years.