The Old Man's Hundred-Year Blessing
An old man greets a boy with a blessing: 'May you live as long again as you have lived so far, and then as long again as your age would be then, and then three times that age — and may God add one more year so that you reach 100.' How old is the boy right now?
Reveal the answer
8 years and 3 months. Doubling that twice gives 33, and 3 × 33 = 99, plus the one extra year makes 100. It's one of Alcuin of York's Propositiones ad Acuendos Juvenes (c. 800 CE) — a twelve-centuries-old riddle disguised as a birthday greeting.