I, personally, feel that 'Supernatural' isn't exactly scary. I mean, it's got horror scenes in it, but the worst that there is is jump scares. The first season is probably the worst for the horror, the others are more about the storyline. Speaking of that, the plot is absolutely flawless. I'm currently starting season five for the first time and the plot has grown and grown and grown into something so amazing. Also, the episodes come in varieties. You get, roughly, three episodes in each season which are humorous and the others are meaningful. Dean does mention some sexual things and I've come across three scenes which are explicit in that way. But, honestly, nobody's stopping you from skipping it. That's what I do, I never miss anything important. But, I'm dubious that the plot - along with many other things - will become slightly tedious by the time the tenth season rolls around. I mean, you've got to have a very talented writer to pull that off. Also, I forgot to mention, that there is lots of violence such as shooting, stabbing, assaulting, swearing, etc. Which is basically expected in a TV series which is labelled as, 'Supernatural'. Overall, I think it's great for everyone over the age of thirteen - even adults!
Also, I know that I'm twelve. But, hey, I'm not bothered with that stuff and I watch it under parental guidance.
Rated for mature twelve year olds.