Paris Venus was feeling old, lonely, fat, and depressed when Senior Friend Finder popped up on her computer screen. A dating site for old people? The lowest tier of membership was free so she filled out a profile, listing her age as 61 and noting she was widowed. For sex, she wrote, when I get a chance before adding, okay, female. For weight, she said generously curvy. She also started sharing some of her deepest thoughts and...