Stories vary online about the origins of this. It comes up in French in the early 20th century, and apparently American newspapers earliest in 1931.
What is the earliest known examples in the English language? Or maybe the concept was borrowed from something earlier, than as an ideal age match-making rule of thumb?
- http://www.onehalfplusseven.com/home/about-the-half-your-age-plus-seven-rule (the concept even has it's own dedicated domain name.)