Er... I don't think I wrote any horror/weird/creepy stuff before I was ten. Although I loved The Armada Books of Ghost Stories, Mike Moorcock's Elric stories, and the creepy bits of the Narnia books before I was ten.
By the time I was eleven I was writing stories for school crawling with Vampirism and Lycanthropy, and doing a sequence of drawings of severed heads on plates (mostly through laziness, because it meant I could skip drawing the rest of the body). For several years (aged 13-15) all of my stories ended with the Earth being destroyed, because I couldn't figure out how to finish stories. Nobody seemed to mind.
I hope that no-one stops your student from writing or drawing what he wants to.