I was a childrens gymnastic instructor and also tutor to others training as gymnastics coaches. Up until I was 65 years of age I was happily still taking the warm -ups in the gym each day. After that I ontinued to do approx 30 minutes of stretching and aerobic exercise at home each day. Could still get down in splits at 70 years old.!!!
This started to tail off in my 70's. Found myself getting breathless just walking to the nearby bus stop. Stairs became a problem, particularly in the evening. Arthritus coming from lower spine caused problems in virtually all my joints. Now, at 78 yrs I have become more and more sedentary. Now use a mobility scooter to get around. Still do my own housework, but in very small doses.
My best friend was a fitness fanatic and attended the local gym 3 x a week, also ran most mornings for a good half an hour. Did a marathon when she was in her early 60's. Watched what she ate, remained slim - and died just a few days after her 70th birthday!
Whereas, I would say, that some sort of healthy life-style does help with us growing older (those who want to) , think it is so much more to do with genetics than anything else.
I have absolutely no desire to live into my 90's - and just become a consumer of things which should be available for the younger members of society.