Some people care about age and maturity that comes with it.
completely true, but do note that there is a rather large amount of ragers that play league. Ive had to sort through 2x year olds who my team has deemed not qualified due to raging. For a proper team to succeed no one wants a rager on their team.
Not to mention,some teenagers are much more mature then some adults. EDIT oh and to help TC. http://na.leagueoflegends.com/board/forumdisplay.php?f=23