I think one of the reasons 30s>20s is because a lot of people have unreasonable expectations of themselves when they're younger and 30 is that mark people like to set as the deadline for all those achievements.
That stress in the 20s trying to achieve those lofty goals really effs you up.
Then come the 30s and while you "failed" your goals you realized "Hey, I'm in a pretty good place in my life so what if I'm not where I expected to be when I was younger, I was naive then. I should enjoy this".
I made a list of goals for myself since 8th grade (probably earlier), and while none of them were strictly "before 30," I still got all of them. To be fair, they were not lofty goals at all. I wanted to be married to someone I loved, finish a graduate degree, and have a decent career. I was never the kind of person to have any unreasonable goals, haha. As far as my father was concerned, my one goal in life should have been to be married to a nice guy who would take care of me, SO....I exceeded his expectations apparently.
I still have more goals I want to accomplish in my life, but again, no firm age and nothing too crazy. I'm realistic :p.
30s are better because you probably actually have a little bit of money to spend
Yes, this part is nicer, but I find I'm more careful with money now than I was in my 20s.