As far as I'm concerned, at 65, I bought an ebike kit 2 years ago to wander about on when I retire:
15 months later I moved to an Ezee kit on a trekking bike, purely to give me more assist on hills.
I'm now retired & averaging 100+ miles per week.
I'm a reasonably fit bloke for my age, but have no interest in over-excercising just to prove something - to whom? The bike is not a sport accessory - It's a means of getting about a beautiful (but very hilly) part of the country without using the car & making enough effort to reap some benefit.
One thing I have noticed though, is that, since I've regularly been doing the increased mileage, although my lower-body muscle-tone has improved markedly, I'm going to have to start controlling my calorie intake, as I've stopped losing weight
I assume my body's adjusted to the increased activity, the same as "Her indoors' " does when she indulges in a spell of that there Yo-yo dieting.