I wonder if this article isn't putting the cart before the horse. If you're not getting just older but also sicker it gets harder and harder to drag yourself to work each day.
Or, to put it another way, maybe you're working at 75 because you're not sick instead of not being sick because you're working.
I'm in my thirties, and already have some mild chronic health issues that make me not really want to go to work some days. I imagine at 75 it's going to be nearly impossible to get me to go in to work most days. Hopefully everyone lives 24/7 in a VR pod by then.
Or, to put it another way, maybe you're working at 75 because you're not sick instead of not being sick because you're working.