Understanding John Mayer's Reference to a "Quarter-Life Crisis"

My recent realization of the fact that I've been on this earth for two decades was borderline terrifying. Coming to terms with the idea that, come next year, I'll no longer be covered by my parents' insurance, that I'll have to get a "real job"-- or go to law school--, that my lazy summers will be over, and that I'll have to start searching for an answer to the question, "So, what do you want to do with your life?" isn't going to be easy.

But then this weekend, after watching a climbing documentary, I began wondering if any of the aforementioned things were even necessary. Why can't I just take a few years off and backpack/climb around Patagonia? What's the big damn deal?

I've never done anything the "usual way" before, so why would everyone expect me to do the same now? I'm in no hurry to enter the real world, and yes, while money is an issue, I could always just rake up some dough and spend it all on travel. After all, when else will I have that opportunity?

So my question is... what are your thoughts? What's the big damn deal if I don't "make something of myself" for a few more years?