The good news is that as we became independent from our families and the institutions that we were committed to, and found paths in our work and family life to be productive, the majority of us became totally normal, functional people. Would I say "happy"? Sometimes but certainly not always - for almost all of us. Life has its way, with health and work and family issues that larger social or economic issues will never have any influence over, regardless of the era you grow up in.
But this article says that people are least happy at 50. So, I'm 50. Am I happy? Not, like, happy happy. But am I OK? Yeah, sure, I've figured things out, have my own family, it's all turned out OK.
Am I happier than any point in young adulthood in the late '80s and early '90s? Absolutely.
This whole "best years of your life" as a teen or young adult thing is... nonsense. It has nothing to do with the possibilities of the human experience. For some people? Sure, let them have their fun. But I don't want to sound like Dan Savage, but, for everyone, it can get better. Chart your own path, work it out for yourself.