The mods can correct me if I'm wrong, but it is not a zero tolerance policy specifically related to age, rather a rational policy regarding models, advertising and public imagery. Keep in mind that though many people consider 18 to be the cutoff age, if this is based on US laws (which vary state to state) the legal age of consent is 17. You'll also note that there is a section entitled Development Models, specifically for models under the age of 17.
Quote by Prettyphile regarding kids/pre-teens:
"We want to make it abundantly clear that on Bellazon, we uphold a zero-tolerance policy when it comes to any inappropriate behavior or discussions regarding younger models. The solicitation of information pertaining to their identity, the initiation of threads centered around them, or the dissemination of images related to young models is strictly prohibited. This unwavering stance is grounded in our unwavering dedication to cultivating a respectful, and secure environment for all members of our community."