Thanks for that, Dr Benjamin. I used to be a bit faster back in my sixties. Even now I can complete a two-mile run in under 17 mins. That's on a gym treadmill, however. The thing about treadmills is that once you've set the time, you WILL do that time, come what may. Out on the bricks and mortar, however, I'm lucky these days if I don't stray past the 18 min barrier. But I keep going.
Generally (to state the bleeding obvious) other activities like walking, cycling and swimming can also make the difference. Regarding swimming itself, it's always encouraging seeing people in their eighties taking their morning dip at our local pool. Mostly they're not fast, but they keep going (as I do) which is the main thing. It also serves as a reminder that exercise can be a lot more rewarding than simply watching sport on the TV, for instance.