I don’t agree here. Playing for long time means you get better, more experienced as well. Reaction time is not all. Plus the differences of reaction time we talk about is usually only important for world class players. Normal humans like us are similar in reaction time between the ages we talk about (30 vs 20 in example). Lot of older people are playing and are better than younger people.
Having said this, every human is different and will have different degradation or changes in their body and mind. I am just generalize here, knowing that individuals might differ strongly. Have in mind, I am talking about normal players like us, not professionals or world class players, where differences in weakness are much more amplified.
And off course it depends on the games as well off course and in what rank you are. My point is that age is often an excuse without realizing the real issues, pointing it to reaction times and aging, when maybe something different is the problem.