SOUTH PORTLAND, Maine—According to a 2015 UN report, the global population aged 80 or older is expected to grow from 125 million in 2015 to 202 million in 2030 to 434 million in 2050. In 80 Things To Do When You Turn 80 (978‐1‐4162‐4610‐7; $16.95), a new book from...