As someone who was vaguely involved, the impression I personally got was that the teenager restriction was a thinly veiled "no more homestucks/voltrons/anime teens" restriction. I just straight up don't think the mod team was thrilled with the canons that were becoming popular in game but didn't want to say so outright.

It's a shame because most of the players affected were really fun and enthusiastic. As someone who played an adult from a canon that was more likely in the mods' wheelhouse, I wouldn't have wanted to stay anyway if those players felt pressured out.