Anything that happened in the first 60% of your life happened when you were young. Your youth expands as you age.
Society labels you, young or old depending, on those around you. If you live with lots of elderly people, say in Florida, you can remain young longer. If you work in the schools you become old faster. More generally the baby boom enables an extended youth for the following generation.
If you wish to feel mature hang with the young. If you wish to feel young hang out with the old. A similar trickworks for wealth, and status.