I am old and the games are getting faster.
I’m getting close to 29, and I noticed it most when I downloaded the NES version of *Punch-Out!! *a few months ago. I used to be able to get to Mike Tyson with relative ease, only to have my ass handed to me (that’s one game I’ve still never beaten), but after I downloaded it I had a hell of a time getting past Soda Popinski. Not sure if I even managed that, now that I think about it. I really want to get *Punch-Out!! *for the Wii, but I’m concerned that it’d be a waste of $50 if my reflexes have slowed that much.
I’m 32, and I’m not as good as I used to be, but it’s not really reactions (well, not all of it), but the lack of practice, as others have mentioned. With a young daughter and work, I don’t get to play video games that much. Maybe one or two hours a week, when it used to be a couple hours a day.
The only reaction I’ve noticed slowing is my “throwing the controller” reaction. Some things get better with age 
I’m with Gonzomax, my reflexes are fine, it’s just the games are getting faster. Although I am getting behind the curve with controller complexity. Too many buttons! Pretty soon using controllers will be considered baby toys.
I averaged .281 on the speed testing thing. In my defense, I’m using a crappy laptop thumbpad thingy. Get me on a real mouse and I’m sure I’ll go faster.
I hope… 
Quite the opposite - now, in my early 30s, I’m better than I was in my teens, or even my early 20s at twitchier games.
I still suck at FPSes, but that’s because I don’t really LIKE them, so I don’t play them often, so I don’t really ‘get’ them - but action RPGs, fighters, rhythm games, platformers…those I’m actually not bad at.
Still not competitive - I usually can’t finish the hardest difficulty levels - but I’m actually finishing games I couldn’t when I was younger.