Something else to keep in mind... penetration testing is far from being the only option in the security field. Sure, it's the flashy, hot-topic item that everyone wants to do since you get paid to try to break into people's stuff. Who wouldn't want to do that? That's almost as cool as being a video game designer!
Don't sell the other areas short, though. And realize that, not unlike being a video game developer, there are a lot of other parts to pen testing that may not be very apparent until you're in the field.
- Are you sure you're not causing PERMANENT damage to your client's systems? Maybe that nifty new remote root exploit as a nasty side effect of corrupting a system file or resetting those complex permissions on an application.
- Are you sure you've tested EVERY SINGLE possibility for external vulnerability? If your client pays you thousands of dollars and then three months later is compromised by something you never mentioned, you can expect (at the very least) a nasty phone call.
- Have you provided sufficient documentation about all the vulnerabilities? This is where all those reports you wrote in high school and college will come in handy.
- Have you got hands-on programming experience in a lower-level language like C or assembly? Metasploit and other point-and-click tools are good for speeding up the process, but you want to be sure you really understand WHY things are working the way they do. (Protip: go read "Smashing the Stack for Fun and Profit" if you've not. I've never seen a better write-up on how buffer overflows work.)
- Do you have experience with Windows systems? Good. How about linux? Ok. How about AIX, HP-UX, or Solaris? Cisco IOS? Multi-platform knowledge is fundamental to getting the big picture. Again, your client will want to know about EVERYTHING you find, not just that you were able to Hax0r their old Windows 2000 web server.
I don't work as a pen tester; I never have, and I doubt I ever will. However, I do work in security, so I like to think I have a bit of the mindset that you need. There are plenty of other cool jobs in the field; don't limit yourself. Keep an open mind, especially while young, and you'll benefit from the added experience. You'll find where you fit in.