When your son's teacher is younger than your oldest child.
When you realize that one hair on your chin has multiplied to 7 and no amount of tweezing or waxing makes them go away. Why don't they turn gray? No, they stay has dark and as stiff as horse hair.
When you find a gray hair in your eyebrow.
When you wake up in the morning and do the scrunch walk for 50 feet to get standing up straight.
Oooh, this just happened to us. At a work function my friends were looking around and commenting on how it seemed that the company is bringing in more and more college interns. Then I said "no, I think those are just regular employees....we're just old." It was true!
Last Sunday I actually did have a getting older experience. The children's choir was singing up front in the church and I discovered that one of the little girls was the daughter of a "boy" I had in my first grade Sunday school class many years ago.