Responsibility makes people panic until they get used to it.
I mean, imagine being 23 and responsible for the livelihoods and career prospects of some 20 people. Wouldn't you panic?
Being told things (at any age actually, think of having a conversation with your doctor about a medical problem) allows you to frame and put things in perspective. The perspective is what is important and what can be very helpful. So a more experienced person (who could be older or could have just gone through the hoops) tells you "that's not a problem in fact here is a similar situation ...".
An example is PG's "How not to Die" where he says:
http://www.paulgraham.com/die.html
"We avoided dying till we got rich.
It was really close, too. When we were visiting Yahoo to talk about being acquired, we had to interrupt everything and borrow one of their conference rooms to talk down an investor who was about to back out of a new funding round we needed to stay alive. So even in the middle of getting rich we were fighting off the grim reaper."
To add a few more, Marx was 29 when he wrote the Communist Manifesto and Fidel Castro was 32 he successfully led the Cuban revolution.
That means they don't found companies as often.
This is not a criticism of 20-somethings who leap into startups--there is no better time to do it--particularly because some of them succeed, and then we all get nice things. But it is in the nature of startups that the odds of failure are so high that the kind of level-headed, staid, steady, sensible person you'd really like to be running a company is the kind least likely to be running it.
It's not great for the 20-somethings, but in this model they're essentially considered disposable; burn out as many as you want, a new crop always comes along next year.
Hell, most struggle with something as simple as losing weight.