It’s not just the loss of brain white matter and myelin with age, it’s also the “generational thinking” that the parent eluded to at the end of their post.
The world has changed radically from the time that you (or I) went through our formative years. We may still perform cognitively, but eventually our software is from an obsolete and bygone era, and we must admit that we’re just not in tune with the more contemporary zeitgeist.
It happens with every generation. Science has a saying for it: that it progresses one funeral at a time, because established ideas must physically die with their owners to make space for disruptive thinking.
Henry Ford used to disallow “beat practices” in his factories because he wanted new guys to repeat the same failed ideas and experiments that had been tried before, without being discouraged to do so. The practical reason is that the world changes, and things that were brushed off as not working some 20 years ago can suddenly start working due to a context change.
A generation lasts 20–30 years, and yet in politics it lasts 40–60 years. Those dinosaurs in politics have no actual grasp of how the rest of the world has evolved around them. They don’t understand tech, or climate issues, or academic inflation, etc. They still apply recipes from a bygone era in which they were actually skillful and successful policymakers, but that era ended long ago.