As the article hints at the idea of an "adult" is closely tied to the structured, 'on rails' lifestyle of the industrial age. In rich societies people live on a linear track: vocation/uni, job, marriage etc.

When I lived in China I met a (physically) older guy in his 60s at the time who had lived through the cultural revolution, spent 8 years on a farm, went back to school when the universities opened up, started a business, then lost the business after various reforms during the Deng era, and had started work as a programmer in his 50s. He always said "when you're younger than 60 you can just start over" when he heard young adults having existential panics.

The guy had restarted his life so often he genuinely seemed like a curious kid, and I think that has a lot to do with just how chaotic and cyclical everything was, he was just used to it. You reinvented yourself every 10-15 years because the world changed.

And I think that's an important lesson because the stable environment that convinced people they're finished adults by the time they're 25 is about to be over everywhere. The whole house, golden retriever, 9-5 Truman show thing isn't coming back and having a childish spirit might very well be a big advantage.