As a minor (13), I very much support this. I like PaperTsubaki’s idea of nsfw tabs rather than completely 18+ characters the most, but I’ll take this in any form. I’ve seen some pretty disturbing profiles and descriptions for characters, that I definitely didn’t need to see, and tags/image filters are used so inconsistently, they’re useless.
Nsfw tabs would be best, mostly because I love viewing characters and reading their bios, and I don’t care for the nsfw details. It could also help with characters’ galleries, and keep them interesting. Character galleries tell stories, and it would be nice to see a gallery tell a story... without sex scenes. Those can be extra for the ones who are interested, I’m not one of them.
Another thing that would be nice is a “sensitive content” filter for things that aren’t porn, but still distressing could be filtered, and not as 18+. I actually like looking at body horror characters, and studying vent ocs, it would be a shame if they were in the same category as nsfw characters, because they’re so different and there’s nothing different about how the average 13 year old would feel about one compared to the average adult.