Guess I'll chime in as well. Here are my observations, bulleted for the sake of clarity and the fact that coffee hasn't quite kicked in.
- Although age isn't a guarantee of maturity, the odds are better that someone who's older than, say, high school-college age, will be more mature. It's not always a given, but the odds are pretty good. My youngest kid is 12. He's soft-spoken, considerate, a real party supporter, and just an overall intelligent and nice kid. The only flaw I've seen him have is that when it's his turn at initiative, he ponders his PC's move in the same way he ponders the move of his next chesspiece. Behavior-wise, he acts better than some gamers twice his age.
- Someone, I forget who, once said that stereotypes exist because somewhere down the road there were consistent forms of behavior/characteristics observed in a particular group of people, and the image sticks. Naturally, pre-judging people is ignorant and wrong, and automatically assuming that just because someone is: (black, Christian, female, gay, or SF fan) they will automatically conform to that particular stereotype is unfair and very wrong. But I have indeed gamed with/dealt with a plethora of gamer stereotypes, ones that I'm sure many of you are familiar with. However, those people to me are the fringe, and they're the ones that I inevitably clash with (or vice versa). Look at Knights of the Dinner Table. You have stereotypes there in a major way. So, while it may be unfair to designate ALL gamers as a whole with a certain stereotype, there's some reasonable cause to consider certain gamer schools of thought as having a particular stereotype. Does this make sense?

I don't know if it would be opening a can of worms to wonder aloud about the various stereotypes that exist in gaming, and discussing them...
- My RPGA experiences were limited to the group as it existed about 10 years ago. There were some really terrific people there, and some real butt-heads. Has this changed?
- Response to Gruff's original post: Someone said, again I forget who, "A joke that hurts ceases to be a joke." The response about you needing to get a sense of humor is one of the oldest dodges that people use when they're getting out of line.