A few days ago I was reminiscing about some of the old friends I had had in my youth. By old friends, I mean people who were in their 60s and 70s when I was a teenager. It occurred to me that this would make them all either centenarians or dead. I surmised the latter. This morning I discovered that one of my school headmasters had passed away in April this year. He hadn’t been one of the mentors I’d recalled, but he should have...