I'm 27 and for me, the most important thing I've learned is that there's always more for me to learn. Even on the subjects I think I know very well, there's always something more.
I don't think people are necessarily any stupider these days, but instead I think ignorance/lack of knowledge and refusal to accept that you might not know everything there is to know on a subject are glorified to an unhealthy degree.
And that I will blame on this fucking ridiculous "there are no losers, only second place winners!" bullshit that parents are raising their kids on. How in the fuck are you supposed to find motivation and information on how to improve if you "never failed"?