Unfortunately, for those for those pushing for a specific age (65) without scientific research to back it up, the study you posted showed that airline pilots brains operate at a significant difference than the average officer worker. As you mentioned sometimes it starts in one's 50's. So is ALPA pushing for mental testing starting at 50 to establish a baseline functioning level and to define when anyone's performance as a pilot isn't good enough so they should be forced out? That's the ultimate standard - can they perform? Age increases the odds of performance difficulties but it's not a cut and dried decider.