All 100% true.
Coming up about to break the 30 mark and I can cosign everything said here.
My early 20's were shifty, some years were better than others, but from 20-24 most people will be dealing mostly with education and career kickoff. Lot of drugs and sex and vacations in these 4 years, all good things, but in moderation. If you make it through the fire, then great. Lots of people get "caught up" in this period.
25-27 most people(who weren't born with silver spoons) are now enjoying their new careers and being able to breathe a bit.
28-30 are the years where you begin to really make your life about what you want it to be about, outside of work and money, because (unless you're a money head) you see it's not all that there is to life. The level headed people usually start families or get involved teaching, charity classes, traveling extensively, etc around this point. Most people have enough knowledge to spot certain types of other people by this point, which is akin to what Face said "Most peoples friends drop off and you get new ones"
I was in school till I was 26 (Bachelors and MBA) and saw a lot happening, but most of the scripts were the same. The people who were always tired from 20-23 from working all the time, were beggining to find happiness, seeing that their efforts were worth it, while the world came down on the heads of the people who never really got it together. I almost didn't go back to school because I thought 25/26 should be nonstop partying(especially after seeing how my associates were living, they were going crazy out in the streets
) but I stayed focused and 27 and 28 have been the best years of my 20's by far
My age now, is when people start to get genuinely satisfied about thier situations and thoroughly optimistic about thier futures, or they start getting bitter. Something interesting that Face said in his post was about "all the stuff people did in thier early 20's is lame in thier late 20's", which is true. But the thing nobody tells you(or at least told me and I had to see for myself) is that all that stuff that people did in thier 20's?
It does not leave them. They have all those memories and experiences inside of them, so if they got into a bunch of nonsense or screwed over a bunch of people, etc, then it will take a toll on their relationships and mind.(unless they're a sociopath) I truly learned that that's why some people (and not be jaded, but mostly women) are legit crazy when they hit 30+. All that stuff they did in thier 20's screwed up thier minds. Men are the same, but just in a different way. That's why some no-good women keep a revolving door of users and abusers and working dead end jobs, and some men are basement dwellers who prey on hoodrats, while others wake up every day excited about life and looking forward to thier relationships. So try to make GOOD choices in your ealry 20's so that your mind can stay well, on into your late 20's and 30's.
Get a solid degree(or two) in a solid field, from a solid school, stay away from low brow women(try not to fall in love with them either high brow or otherwise), don't have kids, work out(you don't have to be swole, but be in shape) and save your money.
You do all of those things in your 20's and i'll say theres a 95% chance that when you hit 30 you will go
.
...carefully read everything he's said and store it in your head for reference. He's %100 on everything he touched on.
in my 30s.
staying in school til your 26 
Im not your Auntie or your mother telling you to go to college. Im saying, you need to learn a skill or get a degree. Please take your ritalin so you can step up your reading comprehension.