I disagree. As someone who spent all of his 20s building businesses, I can definitively say that I lost the most valuable thing anyone has: time. Sure, the experience is good, but its not as good as having focused myself on other more productive things.
Contrary to what you may hear on TV or here, businesses are not made of candy. It requires sacrifice, hustle, and a huge amount of time. Time better spent living life. Young adults don't get that. They think its like Hollywood portrayed it in the Social Network. Nope. It is pretty shitty actually. Even if you join something as good as YC, you still have to hustle a great deal without any guarantee whatsoever. Problem is that what you are gambling here is your life, investors just gamble money. Money comes and goes. Life, not so much.
Then why am I building a startup at age 33, when I already have a successful business? I'm a flip floppin' paradox. Sometimes we do what we do because thats what we know how do to. I'm too dumb and old to do anything else (best guess).
This is no longer true. A couple of years ago, college seniors graduated with an average of $25,000 in debt. And that number is growing. What this means is that the percentage of people who have "nothing to lose" in their 20s is shrinking rapidly. Instead people are seeking "safe" corporate jobs in order to be able to pay off their debts. Working in a risky startup is not a realistic option for them.