You make a very good point. There are other groups e.g. bankers, but they tend to be privileged groups. This point was made to me quite memorably this Christmas. A local group was collecting presents for orphans. I brouyght in two boxes for kids the same age as my daughter. In the whole community, 14-16 year old boys got one box. Next year, I plan to get something for them (if only I can figure out what a 14-16 year old would like that doesn't require power and will fit in a shoebox).
The 14-year old CoD player is, however, not just a stereotype, but pretty much the archetype of what happens in online communities that don't self-police behaviour. The standard of discourse engages in a race to the bottom, where shouting beats listening.
This isn't necessary, even in Shooters: I used to play Unreal in an online community back in the day, and the chat was friendly ("played", or "well played" was one of the standard things you said when you got shot). Even the taunts were actually funny (often Monkey Island references). However, that's a long time ago: I don't find online shooters a fun place to hang out anymore.
I have no problem with the idea that in this community, Paul Graham is the best role model for communication. But let's not pretend that the place is flawed purely because of it's demographic.