For me it was learning to downhill ski last year. I always figured it was for 20 year olds.
Speaking of 20 year olds, "the hobby" comes a close second.
What great thing did you discover in your mid-life decade?
I agree the hobby is an insanely cool discovery. Sex is now always available. What a concept. Good thing for the wallet I didn't discover it too early though.
Financial security, knowledge, leadership, self-confidence, the feeling to have accomplish something, memories, experience, matiurity, know-how, to feel handsome.