I honestly really think that should be checked by default.
Viewing post in Delete all ADULT games
While itch is not aimed at kids or teenagers (like gamejolt apparantly tries to) default setting to on would be just wrong. That stuff is for opting in, not opting out.
(Itch is aimed at people wanting to play or create indie games. That is not something I would attribute to teenagers in general. But maybe I am mistaken and some kids do not play on their xbox yelling insults at strangers ;-)