21 years, but I was newly married once and remember thinking I was coming up with something new(every once in a while) till I watched some old stag films and figured out that they all had it figured out some time ago! Some old guy gave me a bunch of stag films from the 50's back when I was in my 20's(some 30+ years ago) and I would let my friends watch them and when they got real interested in what was happening I would casually mention that all of those women were 90+ years old now.