I know a number of people under 22 that have their pilot license. While not a huge percentage, not rare either. And the initial time is not that long at all.
Additional anecdotal data: of the four or five pilots I know personally (ages 23 - 65), all had their pilot's license before turning 18. So, yeah, not all that uncommon.
Note: I'm not a pilot, these aren't coworkers, just natural friends.