Last week, an old mate came to stay, along with his wife and seven-month-old baby. Sam was the last of my university pals to become a parent. For years, while the rest of us were shackled by domestic responsibilities, his Instagram feed had shown him merrily gallivanting between music festivals and exotic holidays. Now, at the age of 47, he’d finally settled down.

On the second morning of the visit, I found him limbering up to go for a run. He admitted that he hadn’t done any exercise for ages, despite having always been a keen runner.