As a parent I wouldn't want my child in any mmo unsupervised until at least 16 and then only if they were involved with people I knew and trusted. Even at 18 you're only an adult in numbers and you have a LOT of growing up time to do.
I prefer age restricted guilds myself as I find that this is my escape time and I don't want to have to worry that I'm corrupting or upsetting someones child, much less have to deal with the inevitable temper tantrum that always comes with most players under 21. Nor do I want to find myself standing in as parent when 'yours' fail to notice your behavior or the fact that you're on line at omg-o'clock.
You have a valid point OP but you're going to find that most people really don't feel comfortable with the restrictions that playing with younger gamers puts on us. An example, when Second Life merged the Teen Grid with the 'Regular' grid. They put safeguards in place to keep younger users out of some areas and this failed horribly. You find, should you log in there that now you are not at all comfortable with an adult RP situation unless you see a valid photo id first. Now not all servers are RP, and not all people do things of a sexual nature in mmos, but even causal flirting becomes creepy when you could be the parent/grandparent of the person you find yourself talking to.
Also as a parent, where ARE the parents of most of these kids, I have a schedule that lets me play late in to the night and early morning and I can name at least 5 under 20 who are still in school and are still on at 3am or later on school nights.
I'm 39 and my generation was supposedly raised by television, gods helps us all if this generation is raised by computers and the internet. Granted it would explain a lot of the behavior I've seen in all the ones I've played. ( The Realm (bet no one remembers that one) to UO to DAOC to COH/COV to WOW to EQ II and back to WOW, so I've seen a lot of younger players and I've seen a lot of why people want age restricted guilds. Yes, it's exclusionary and may seem unfair but guess what darlin, life isn't fair.
Are you dedicated? Tired of Pugging? In at least Black Hole/Rakata mix? If so then we want you! We're looking to put together a second progression raiding group and we need tanks and healers asap. (will take DPS as well, we just like people) You would need to be willing to commit to two to three nights a week, for 3 hours on those nights, We'll give you fun, friendship and content progression! We are an imperial side guild and one of the two top progression guilds on that side of the server. Whisper or mail Phaedrah or Kassnja in game and check us out on our website! http://sev.enjin.com/home Hope to hear from you soon! Kassnja