When you're young, grown ups tend to judge how mature you are based on your dreams for the future.
The small boys and girls, dreaming of becoming princesses and astronauts. When you get a bit older, it's pop singers and rock stars.
Then, a few more years later, you want to fulfill yourself, most often in a creative or economic way. You dream of being a famous artist, writer or photographer. Or the Vice President of a successful company, of starting up your own sky rocketing business.
Then you start to see the way of the world, and you realize that perhaps the judgment passed on your dreams wasn't that far off. That they were based on your lacking of a realistic view on the world. On the knowledge that everyone can't make it to the top, because there are millions of struggling artists in the world, millions of power hungry and competent business men. And the realization, that most of them are so much better than you.
And then, once this has dawned on you, you start to pass these same dream based judgements onto others.
Because the truth is, it is very noble to follow your dreams, but you need to create security around you in order to survive that day you realize that it's a hopeless cause.
That's when you need your regular job, in a regular office, doing regular but hopefully interesting things, making enough money to support your dream chasing in your spare time. Never giving up, but not stopping your life from moving forward based on a far fetched dream. That, in my opinion, is when you are grown up.