Past twenty I did not have a big opinion on old or young ages any more.
A friend of mine, way in his nineties, said that he had thought he had been old earlier in life, but when he hit 80, he considered himself old. Everything under 80 was young to him. That watershed did not change for him when he grew older. To him I'm a really young whippersnapper.
Don't really think that sort of perspective can have much meaning. Saying anyone younger than me is young, and anyone older than me is old, allows no meaning for the words. If perspective is relevant, then it would be personal perspective. Can't imagine many people in their thirties count themselves among the youth.
For him there was the observation that age related problems became very real after 80. He saw that among friends, and noticed it himself. So a perspective based on existing as a person without procreative needs.
Think that has changed perspective on age a lot. A few generations back you had to procreate between twenty and forty/thirtyfive, after that you were fit to be a grandparent, if still alive. Now people are productive in other ways than getting children for most of their lives. Age gets a different meaning.
Do people in their thirties see themselves among youth? Lots of them do, I think. The "harden the fuck up" and the "grow up" is way less impressive than the lure of eternal youth. Forever young. Music, clothes, facelift, beauty products.
The "oudere jongere" (elderly youth) is disappearing.
Here's a wannabe elderly young person for you from the eighties. (satire)