Maynard will probably come in and curb stomp me for saying this but I think its up to the admin to issue a warning to any underage kid that talks non stop or enough that it distracts from gameplay.
After that fact I see no issue with temp mutes... now for the record I said temp mute don't put a perma mute on them just because they are annoying.
Its also your job to explain to them that team related info is ok but I don't wanna hear your 12 year old voice arguing about which is the best pokemon.
While we have no official rule on this at ibis look Counter Strike is a what Mature/Teen rated game... that being said if your under the age of 16 your probably shouldn't even be playing it.
We don't enforce an age rule in our servers but I have run into my fair share of kids that just talked to much.