I gained my CPL when I was 18, and that was in 2003. First job a few months after that. I don't think I ever put my passengers lives at risk simply because I was only a youngen. And I was PIC.
Yes there are some stupid 18-21 year olds out there, but I've found most of the 18-21 year olds I've come across, and hold a pilot licence, are fairly level headed people who hold just as much credibility and maturity as those who are 25+ years old.
On the other hand, I've met some awfully stupid pilots who would fit into the 30+ age group.
morno