In response to the players here seeking an English speaking guild with RaidCall, we have that. As far as "Mature" goes ... which definition? Our ages range from Teens to 40's & span a lot of interests. We joke around a lot in game & discuss many topics. We enjoy using RaidCall when grinding in dungeons & participating in PvP. Our goal is to NOT take the game too seriously as that would ruin the fun.
That said ...
If that is what you mean, then you must be level 20 & a member of the Realm Eos. As for our RaidCall, you can find our ID here
good Luck & Enjoy the game.