As I recall John Miller flew his Bonanza until age 101 (the last few years with a safety pilot). It may have been his 35000 hours in a cockpit. Or it may have been his time in the Kellett KD-1 or his own Pitcairn PCA-2 that kept him young.
Dick DeGraw designed and built this,
Here's some background info on Dick, including some earlier designs,
You can PM user All_In to inquire about contacting Dick Degraw,