The best pilot I've ever flown with was a designated examiner for the FAA and he was 70 years old (at the time). He use to teach in B17's at Minden, Nevada or other similiar bases.
Great hornet. As soon as the world's pilot force gets to pick and choose the amount of flying they do each week, as well as the type of weather they fly in as in you examiners case, then the safety risks of elderly pilots will drop significantly.
Most of us on both sides of the issue can point to certain pilots who are as sharp as they were in their 20's and far better with their experience. Abritrary numbers are a fact in every aspect of life including aviation. They exists because it is prohibitively expensive to micromanage every single little detail in the lives of many people, including the skills of those who want to fly without an age limit.
Just keep dancing around reality folks.