Dudley, I am sorry to hear you lost your medical as I have always wondered when I would lose mine.
Now the status of my medical is being able to get up every morning and not feel any older or physically worse than I ever did, I still pass my regular six month medical for my ATPL only because I want to know the way my health is tracking not because I need to to earn a living flying.
Every time I see a picture of a Pitts or some other aerobatic airplane I wonder how long it would take to get my system back in shape to wring one out and then I realize I am getting old because I " KNOW " it would hurt to much to get back in shape.
I now have the best of all worlds for me......my Cub project takes up all of my 20X30 foot garage that has been turned into a hangar heated with every tool and aid I need to work on building the Cub.
As to flying and being an instructor that is not an issue for me anymore until I get the Cub finished and on big wheels, then it will be back to work instructing pilots who want to learn off airport flying.
Age is difficult to measure as we all are different we just have to do the best with what we have.
By the way I am a firm believer that good instructors are born not made.