In 2000, I published a book called “Rules for Aging,” a sort of how-to guide for navigating the later years of one’s life. I was 60 at the time and thought that I knew a thing or two about being old. Twenty-five years later, I just finished a sequel, which reflects my advice for growing very, very old. (I have been doing a lot of that lately.) It took me 85 years to learn these things, but I believe they’re applicable at any age. 1. Nobody’s thinking about you. It was true 25 years ago, and it’s true today. Nobody...