One straight up idea, keeping in mind that hard kink is more than just ageplay, and if you’re going to talk about hard kink being sequesteered under content warnings, make it universal.
Give us a color-coding system? Pink for ageplay. Red for violence or non-con. Black for snuff. Purple for drugs. Etc. Then you have tags you can put around bits in your desc/about/LFRP that will automatically hide it behind an opt-in click, color-coded.