I think that’s why they are currently starting a new category of YA that is New Adult. I believe (I could be wrong) that Harry Potter started as a MG. Not sure though.
My daughter read Harry Potter when she was 9. And loved it. I loved Twilight, but wanted to wait until she was old enough to feel comfortable asking me the questions that could arise from reading Twilight. Namely about the sex scenes. And weird stalker/love relationship. She’s 11 and I’ve seen this level of maturity in her behavior, so I recently let her read the Twilight books. They did bring up questions, but not nearly as much as I thought.
And she didn’t care for the first book because it was “too much” about romance and not enough action. Funny. As you can imagine, the Hunger Games series is her favorite by far. 🙂