I don't believe in the older you are, reaction time is slower thing. A lot of the top players in the FGC are old as dirt. A prominent player who in his late 40s, is sponsored by Hori and is the only player in the world who can play a certain character in a certain game because of the character having combos which are one frame links after another. Well this player can do these combos perfectly every time in high pressure situations against other world class players.
Just imagine you are a bomb diffuser and in order to diffuse a bomb you had to hit a button 1/20 of a second perfectly 7+ times in a row. He would be able to do that like nothing. He's just one example of many though.
The whole reaction thing may apply to other things in life but I don't think so for gaming. This doesn't just apply to fighting games either. World record holders for games like Tetris, old school arcade games, etc are people who are not young.