It's an interesting point, but I've noticed this sort of age discrimination becoming more prevalent recently. People are happy to tar all WoW's younger players with the same brush -- one experience of an abusive fourteen-year-old in Barrens chat blows up into a strong dislike of all under-18s, resulting in "mature-only" guilds which only take players over 30 (for example).
My experiences, especially of the last few months, have shown me that teenage players can be as mature and responsible as anyone -- perhaps more laid-back than older players who have limited playtime thanks to jobs and other responsibilities. Have you suffered from the common stereotypes of younger players? Do you cringe whenever the words "fourteen-year-old" are used as an insult? Or are you happily entrenched in a mature-only guild without a single curfew in sight?