Bittersweet demographics are found in this edition of xkcd, explaining why being single after age 26 isn't the end of the world, but having a firm mathematical grasp of why this is so means you probably need the assist from an ever-growing pool of eligible marital partners.
For the record, someone actually graphed the population of eligible unmarried citizens in the United States based on the age-halved-plus-seven formula used above. (Thanks, reddit.) For men, it's a steady stream of improving prospects until about age 50. For women, the peak is around age 41, probably because men die younger. Thus, the old adage that unmarried 40-year-old women have it tough is statistically accurate. Weird.