I wanted to write a YA novel, truly. My first Beta reader, though, was an 8-yr-old.
Try as I might, I couldn't add anything that would make the book "too adult" for her. Therefore MG.
Try as I might, I couldn't get my wordcount much above 30,000 words, about the length of most Nancy Drew books. Therefore MG.
Try as I might, I couldn't write anything that my "dream agent" possibly wouldn't like. Therefore MG.
Then, finding out that an agent said in her blog that NY Publishers are looking for MG, I celebrated!!! Now, I'm working to get my current edit finished, an ace synopsis and query letter written.