Imagine a very simple "game". You have a black screen. Sometimes a letter flashes on that screen, either A, B, or C. When that letter flashes, you need to press the corresponding key on your keyboard within a fraction of a second. Pressing the right letter within the time limit gives you a point, pressing the wrong letter or being late is a miss. After 100 letter flashes, your score is shown.

What can we say about this game? Obviously it is very easy to understand. Everybody would be able to play it. But how difficult is it? It is pretty clear that this mostly depends on how many milliseconds you have to press the right letter. How would your score in this game improve after playing it for 1 hour, 10 hours, 100 hours, or 1,000 hours? Probably not very much; especially if you are already a gamer and play games in which reaction time is important, playing another game like that isn't really likely to improve that particular "skill" very much. On the other hand, your score in the game is very likely to be affected by your age. Your reaction time slows down by about half a millisecond per year. The average age of a top athlete in e-sports is significantly younger than in regular sports.

While our imaginary game doesn't exist like this, different version of it exist in a large percentage of video games. Pretty much every game that isn't turn-based but real time has elements in which you see something on the screen (e.g. your virtual enemy raising his weapon) and have to press a key on your gamepad (e.g. press B to block) within a fraction of a second. Because there are probably more than 3 keys involved, the stimuli are more complex than a simple letter flashing, and there are things like key combos involved, real games are a bit more complex than my imaginary game, and would need slightly more practice to master. However the two basic truths of the imaginary game still apply: The game would be a lot easier if you had more time to press the button, and your reaction time (and thus age) has a huge influence on how well you will be able to play.

Now these basic truths could easily be used for better game design. Not all gamers are teenagers. I am in my mid-50's, and there are a lot of gamers my age, because video games appeared when we were teenagers. There are even older gamers, who picked up the hobby later in life. But there are quite a lot of games out there that don't sell to us older gamers. Not that we wouldn't want to play them, but because some developer somewhere put a completely arbitrary reaction time limit on a game mechanic which results in the game being perfectly balanced for a teenager, and nearly impossible to beat for a guy 40 years older than that. Why can't we just have a slower version of the same game for us older gamers?

Many games have difficulty settings, but I don't know of a single game in which these settings simply slow down the reaction time sequences of the game. That would be so simple to implement, and it would open up quite a lot of games to an older and slower audience. Why has nobody thought of that before?