I agree absolutely that we are, on the whole, fitter than previous generations. In my case, my parents, who took up hill walking late in life, were very fit, and my Mum was scuttling around on a bike all her life, although she died at 63 from a cancer that might well not have killed her today. Their mothers - my grannies - seemed very old and staid to me. Further back still, I have a photos of two of my great grandmothers; one looks like an elderly Queen Victoria, while the other is posed seated in the garden in long, black clothes, looking like an elderly matriarch, but in fact they were both only in their 50s when the photos were taken. (Mind you, they had each borne about a dozen children! That must take its toll.)
As some people are remembering, my OP was about the ludicrous claim that at 70 we are as fit as we ourselves were at 60, which is quite another matter.
I have just been out for a 45-minute walk; now I'm off to do some gardening, and later I am going for a swim. Just don't ask me to teach a class of tots or teenagers, or drive an ambulance!