AnthonyGA
Well reasoned post. I agree that individual test could select those individuals that could continue flying and some might not make the cut below Age 60.
The problem is that I haven't heard of anyone doing comprehensive testing with medical, line ops or simulators to a level that would truly weed out the problems. Such testing in the USA would face decades of lawsuits even if they were perfectly designed. The problem is resources. We could test individuals faced with arbitrary limits throughout society from young drivers to young voters along with every other limitation, even the 35 year old limitation for the US Presidency. It simply becomes cost prohibitive for society to cater to every individual as in this case.
As I mentioned, I've flown with superb physical specimens who surely could fly to age 70 without problems. I've also flown with more than a few that were lacking and it appeared to be age related, especially when it came to fatigue.
The type of flying is also a factor. Many of the comments I've seen from others here along with my company and US carriers have been widebody Skippers averaging 9 day months with 3 landings, 2 extra First Officers helping if needed and excellent crew rest facilities. It's far different and more fatiguing flying narrow body aircraft into congested US airspace with 3 legs at the end of a 13.5 hour duty day at 2 am.
To repeat, I've flown jets in that enviroment with those adverse schedules with 60+ individuals. At times it was ugly. Some of then sounded like many here, that they were better than they were at 25. Usually that statement came at 10 am with half a cup of coffee in hand.
It is a safety issue. I've seen it first hand.