I know maturity level is more important than age, but I also know any thing taken to an extreme is ridiculous. I have been in touch with an international marketing firm and had been invited in for a second interview. The person interviewing me looked awfully young and was dressed in a very stereotypical suit. At one point he asked me my age (which, by the way, I heard is illegal?) and I answered. I asked him the question back and he said 19. He seemed like a typical 19 year old, for example he talked about how winter is his favorite season as he can go snowboarding then. Now, I'm not saying there's anything wrong about being 19 or snowboarding, but I'm not sure I would be comfortable having someone this young in a management position.
He had some young tendencies that most people his age have. It has been my experience that employers like to hear would google search something to find how to do it, but when I told him this he didn't like it and I remember back in grade school it was consider cheating to "google search the answer" (though obviously in the work place that's what you do).
I don't know how to take it that the second round interview was conducted by a 19 year old kid. Also there was some other questionable circumstances, like how we ended up going to Starbucks for the interview as apparently the office was in the middle of moving.