Well from what I saw, and the sign did say it was directed at middle school and high school ages, most of the kids there hadn't even heard about Kumoricon or any of the meets the forum members pull together. So the library events are kind of like the kick start to their growing fandom, while to some of us...it's just another great day to cosplay.
As I grow older I feel more and more uncertain that I'll be welcomed in a crowd of young fans.
Ironically I carried on a conversation with a girl there who didn't think there was anyone my age that would talk to someone like her. I guess it just shows that knowledge is power.