I would rather dungeon with yourself than some of the asshats I've met through the dungeon finder.

A "children's game"? That's rather arguable, given the themes and events that transpire between level 1 and level 80. I mean, we've (kinda) killed gods and dealt with essentially crowning a new Lich King. That's not even touching on the subject of murdering people over difference of opinion / racism.
That aside, agism occurs because a few reekingly bad apples are always in the mix-- usually teenagers who are just grasping the idea of memes and copy-cat-cool. Having been in several levelling guilds, I've seen first hand the bullying, clique-heavy community of which these turds are capable. No thanks.
I realize that not every kid embodies this particular blend of unclassy, but, having been burned before, I'd really rather not take a chance at this point.

Right on - it couldn't be said any better than this.

Sadly, we see this same problem in a lot of aspects of this game. GS is a good example. While yes, it's true that certain raids require a minimum gear level, it seems just as silly to measure a player's value to the group soley based on their gearscore as it is to measure a player's maturity by their age only.

Unfortunately, I feel like most people just don't particularly want to invest the time in taking a chance on a younger player to find out if they're mature enough.

I used to be an officer in a guild that would accept anyone and give them a trial period. If within that trial period you could demonstrate maturity and some basic understanding of your class(s), you would then become a full member with raid spot opportunities. I guess with this sort of thing you still need to exercize some caution though. Ultimately things got too lax and that started causing some issues later on.

As muagen said, I think that ageism is derivative from generalisations, themselves derived from the poorly behaved minority(?)

But, generalisations have to have some foundation, and I genuinely believe that much like in the real world, a cross-section of the male 12-16 age group would contain a much higher degree of immaturity/aggression that older age groups (presumably due to the phase of forming an individual identity that so many teenagers pass through clashing with an overarchingly anonymous environment, but that is a discussion for another day.)

I disagree with guilds having over-18 limits, but the discussion is not necessarily based around stupidity; rather, arrogance and immaturity. While many younger players are well behaved and mature (like you seemed to be), a degree of scepticism is necessary for guild masters trying to develop a cohesive team because the fact is a large proportion of younger players are simply immature, and the safe (and lazy) way is to have solely over-18 guilds, and that is an unavoidable fact in WoW. However, most guilds are entirely reasonable if you can speak intelligently and modestly, will bend limits to allow you in.

I disagree with a lot written here in this post and in the OP.

First, the average video game player is OVER age 18, so it is not the case that we are playing a children's game. WoW plot lines are quite mature, despite the cartoon-like graphics and not really appropriate for children.

Second, it is inappropriate for minors to socialize with adults without proper parental supervision. Unless they are playing with their parents, which I think is great, it should not be condoned.

Lastly, "mature" teens are the exception and not the rule. I've witnessed teens crying in vent over loot drops (crying!!!), talking endlessly, awkwardly flirting with female players, taking offense when given criticism and then setting off a boss encounter before dropping group.

For any new guild member/trial raider, it is always the case that you need to prove your ability to the rest of the guild. Unfortunately younger players have to prove their age isn't a liability as well.

As for positives, I think kids have more time to actually show up to raids, probably have better hand eye coordination than us older folks, and as Edeese pointed out in his post, won't be showing up wasted on raid night

Same here; though I'd have to admit I was never very good at the game back in Vanilla.

"but simply tell a child of 15 that they are being annoying and politely ask them to stop and they are likely to shut up."

How well does that work for you on Trade or Barrens chat?

I have to agree with you... provided the kid actually listens.

Like a lot of people on here, I was in an 18+ guild before. I'm all for crude humor now and again, but these guys were like the love child of trade chat and X-Box Live.

My new guild is full "mature adults" and one kid. We all got the warning to watch our language around the tyke (which I can agree with), and he raids with us... Unfortunately, he never shuts up. Ever. And it's about the most inane things.
And, unfortunately, the boy's mother was in the raid with us. So, telling him to cut the chatter during a fight led to the mother telling me to shut the hell up, in just as many words.

So, I guess my problem isn't with the kids, after all. it's with their parents.

Yeah, sounds more like the mom needs to take a chill pill, if you weren't rude about asking him to be quiet. If you were, well...don't be.

That said, immaturity is not a result purely of children playing the game. I would dare say there are more immature adults then there are children!

Point in fact, I've been gaming online since I started middle school, across a few games. I've had friends ask me my age and be surprised that I'm 'only a kid' because of how I act.

And yet there are those who insist that I have to be over 18 to play with them because they don't want "a noob kiddy playing around". Sigh.

I have to disagree with the majority here. As a guild leader since before Wrath, I've never had an age limit for joining - people just needed to prove themselves mature. In cataclysm when we start recruiting again, I'll be enforcing an 18+ rule.

During the past year, I've had a lot of members come and go, but out of the 10+ 15 or under members we had join, only one is still in the guild, as one by one all of the others bitched about loot, stirred up drama, talked innanely when we told them not to, distracted our other raiders and generally weren't good players.

The fact that we still have a younger member in the guild means there are mature, younger players out there, but from my experience they are definately not the majority, and when I have to recruit again, I can't be bothered to take the risk. My guild chat is pretty mature, nothing akin to trade chat, but any young teens in the guild tended to make it worse, not force others to clean up their acts.

im in this category and matureity is not the exception basicly no one i play with knows my age. the only reason teens get a bad rep is because the ones who moan and beg and stuff for obvious reasons are the ones who get noticed even though most teens are playin quietly
for instance one of my friends is in a major raiding guild and has never been critisised for moaning or anything like that and they only recently discovered that he was a teen. on the other hand ive known people for a while in game only where theyve been complete idiots and when theyve hinted at there age group people were astounded to find he was in his late 30s. also on the point of the guild with the "locker room" chat then youve naver seen a teenage school with out adults its hardly tea and biscuits polite.

Aside from the bad apples argument, another issue is control over your own time. Both guilds I've been in are 18+ but will bend the rules for mature teens and, frankly, the maturity level hasn't been an issue - you DO need to chat with them a bit before inviting, but you should do that for any player.

The biggest issue we've seen is that teens don't control their time. If Mom or Dad comes in and says 'take out the garbage/do your homework, shut that off and go to sleep/it's dinner time' then the kid has to deal with that. Adults aren't perfect at this, esp adults with young kids who sometimes play when they should be paying attention to their kids... but they control their schedule. They can play for 3 hours at a shot and no one is going to tell them the garbage should go out or that they need to wash the dishes NOW (well, if they're married... *cough*). That doesn't matter when questing, but is a bigger deal when running 5 mans and raids.

Many guilds ask for their members to be over 18 not because of suspected immaturity, but simply because they don't have much in common with teenagers.

While progression raiding guilds may put a priority on playing ability and simply ask for a minimum level of maturity from their members, many smaller social guilds are pickier about their members' personalities. They want their members to be the sort of people who they would hang out with outside of the game. And the outside interests of even the most mature 13 year old are bound to be different than the interests of the most childish 35 year old.

I don't doubt that ageism exists in WoW, but there are entirely valid reasons to not allow children into one's guild that tend to be overlooked.