Just maybe some info on how other parents have made these decisions.
I may be a bit of an outlier, but I pretty much let my kids read anything they want. I'm more cautious with movies,* but I generally think books are the safest place to explore things you're curious about or encounter potentially upsetting content. You're limited to what your own brain can imagine or understand (though graphic novels are more of a gray area here), and it's super easy to skim/skip stuff you're not ready for, or put the book down if it's too much.
*Rose, age 14, wants to watch Pulp Fiction and my answer so far is no, mostly because of the rape scene -- but she also picked up Lolita on her own and I'm fine with her reading that.
That said, there's a difference between something my kids pick up on their own and something I actively provide for them. Jane (who is about the same age as ltc) is a strong and voracious reader and has read a number of YA books, but when I'm picking out books to recommend or bring home for her, I'm usually still getting middle-grade books, not YA. I do feel like YA as a genre has aged up quite a bit in the last 10-15 years, and it's harder to find YA titles that are really aimed at younger teens now, which is a problem.