Do you feel younger than your age? More importantly, do you feel you can, as Susan Cooper puts it, “look again at a mystery through the eyes we used to have?” Because that is the essence of writing for the young: the ability to look at things through their eyes — which are, indeed, our eyes just, as Cooper again says, “not yet wearing our heavy jacket of time.”
If you can put aside time’s weighty coat and douse yourself in the heady perfume of having an entire life yet spread out before you, then you are ready to write YA.