You're looking for some kind of static ideal. And obviously, your idols have been shattered. As well they should be; too bad the ideal remains. By your definition, most elderly people are not mature. Nor is anyone forced into poverty by political economic reasons. Nor some people who have certain chronic illnesses. Nor are people who would rather not raise a family, apparently.
I think the people who are lonely, sad, and miserable are the ones who are most obsessed with the idea of being "grown up" and "mature." What the hell is the point of rushing life if you actually enjoy it? I'd rather be a happy kid for the rest of my life than a stressed out bitter adult.
Yeah, that one is total bullshit, most of them are cranky and miserable The only time you see happy parents is when they have half a football team going and enough funds not to stress the fuck out. The rest might go goo goo for the first couple years then turn bitter when their little brats turn into ungrateful teens
I've been obsessed with these things all my life from a very young age, and I don't foresee that ever changing.
I am in fact not looking for a static ideal, you'll note it is heavily variable based on culture, and situation. it isn't static, but dynamic. just as people are.