Well, I think aging has a lot to do with it as well, as does a lot of older folks playing games, oftentimes having grown up with them. To be brutally honest my hands are not what they used to be, but even before that I noticed my reflexes and reaction times being a lot slower than when I was a kid playing NES and SNES games. I very much doubt I could do a lot of the games I used to play and beat back when I was a kid the same way.
The problem with games nowadays is that making them challenging for all audiences is very difficult, and gaming companies find the idea of creating games that are not for the broadest audience possible to be an anathema, so as a result every game must be objectively easy by even the lowest end gamers.
At the end of the day though being a good gamer has very little value as well because of it. See, nowadays putting in a lot of effort, frustration, or simply time to see things that anyone who invests the same amount of time and effort can see lacks value. You dump say 40 hours into a game you might see a basic story carefully crafted not to offend anyone, and which anyone who put 40 hours into the game can see. Compared to say older school games where only a few would have the persistence to see the end. In old school MMOs like "Everquest" only a tiny handful of people would see the original plane of sky as well, and thus doing so had value. When the only value in gaming comes from being able to do and see things very few other people who want to ever will, and then you give everyone the same experience, one has to wonder what the point is after a while. At the end of the day one of the barriers I think gaming is running into is making the experience valuable, as much as interaction can be cool, even games that tell a story oftentimes run into the problems that there are other mediums which can tell a story as well, or better, than a game can. In short I think games require a feeling of accomplishment to be good, and frankly that can't just come from pointless achievements, or telling a story which likely could have been told a number of different ways. With all do respect for David Cage, I have yet to see any real evidence where a video game is creating more emotion than a movie doing largely the same thing. Pushing X for the character to brush their teeth or whatever doesn't make me empathize with them more... maybe even less if it becomes annoying.