Once, when I was young, I went up Snowdon. It was stiff going and, when we got to the top, we rejoiced to think the hardest part was over, and that it would be easier going down. But it was not. Going down was worse than going up, much worse. It got one in the shins, a knife-thrust for each step.

In one sense, aging is like this. Is everyone in the second half of life going downhill?