The Problems with banning "Sim CP"

[failure_artist]

Let's say you have a site that hosts nsfw art. You don't want it to be overrun with shota/loli. Gross! But what rule do you put in place to keep it out? And keep in mind, this is purely about non-photorealistic artistic rendering. Photographs are a different matter. Here are some possible solutions:

•   "The subject must be 18+"
  
  • Okay, but by whose accounting?
• "The subject must be 18+ in their canon" 
  
  • But what if the character doesn't have a canonical age? What about a character that ages over the series? What if they are of a race that doesn't have a human lifespan? What if the character is chronologically over eighteen but looks like a toddler?
• "The subject must look over 18+"
  
  • What does that look like? What if art gets flagged because a character is too short or has a small bust despite the character being in their 20s or 30s?
• "Older teen is fine, pre-pubescent isn't." 
  
  • You still have the problems above. Plus, if we're treating pictures as morally the same as photos it doesn't matter whether the subject is 17 or 7. 
• "All art is allowed as long as it isn't photorealistic"
  
  •  Maybe the best choice.

I don't really draw much. My problematic work is writing which is another issue. I don't like shota/loli but I wonder if it's a necessary evil or just evil.