This makes sense, thank you both for the clarification.
This is a very good question, and I am a little red in the face to admit I have never thought about it before. Thinking through my favorites like The Worthing saga as well as the Ender series by O.S. Card or the Elminster series by Ed Greenwood, their protagonists happen to be older than the typical YA MCs, yet I think they are still marketed for high school kids.
As Riv notes, those are all old books, so using them as comparisons is a problem off the bat. Also, the Ender series isn't YA. Ender itself is arguably MG or YA, but the series goes off into clearly adult books. The Harry Potter series starts MG but is solidly YA by the middle to the end. The character ages and his problems change. Because h.s. kids are made to read things (or read them by choice) -- those aren't marketed to anyone atm, as far as I know -- doesn't mean they're YA, at all.
Likewise my story I have tried to avoid announcing exact dates and ages of characters, hopefully creating a more timeless story that a larger range of reader might identify with (am I being a dreamer?) However they are still heavily influenced by RPGs and would likely appeal to a high school audience. There is slight sexuality, mild profanity, and detailed violence but nothing you would not see in a typical anime. At around 86000 words I think it hits in the upper end of the YA genral desired length. Other than that, and without being able to post a sample yet, I don't know what else might signify if I belong in YA or not.