You're avoiding the truth that as people age their physical and mental capabilities decline. It is a fact of nature whether you choose to accept it or not.
Why do airlines have mandatory retirement at age 65?
Is flying straight and level at high-altitude require the same physical and mental fortitude as flying a P-51 at 50' AGL and 500mph around Reno during race conditions?
Lastly, why did the USAF put Yeager in a two-holer F-15 instead of sending him up solo?
It's the FAA that mandated that, not the airlines. And it is only scheduled airlines. Cargo has no restrictions on age so long as the pilot can pass the FAA exam. More here:http://www.apaad.org/history.htm