What he refuses to grasp - any of us, even a grandma or near crippled 75 yo man, could do his workouts without blinking an eye or breaking a sweat.   He however, would die and be in the hospital within 15 minutes if he tried anything we do. 
Ummmm...Well I am close to the second example, LOL!  I am not yet allowed (again) to train with weights.  The last time I could do squats was well over a decade ago and I was even then, older than he is now.  I did multiple sets of 20 reps with 300lbs to 400lbs.  I used stands made by my late brother and a pair of sawhorses in the event I could not complete a rep.  My best leg extension at home was 225lbs. for one set of 100 reps.  That was hard, almost as hard as my 100 rep squat with 225lbs in the mid '80s.  I was shaking  on that one, LOL!
Those days are long gone and yes, I have difficulty with but continue to accept that reality, but as Lone Watie would say, I endeavor to persevere!