Twitch reaction time isn't particularly important in most games. Quake and UT, sure, but even in those most twitchiest of shooters strategy will still carry you into the upper echelons of players.

Counterstrike is almost entirely based on spray control and map knowledge. Twitch reactions have only a minor role to play.

Even games like Starcraft are determined primarily by strategy and not mechanical speed. You could probably play at a professional level before a lack of speed compared to your peers would actually begin holding you back.

Plus... you can train reaction time and multitasking. An actual physical impairment like RSI might stop you, though.

The whole "ohhh I can't do games because I have the olds" is such a nonsense cop-out. The rest of your post is pretty accurate, though.