I agree with the people who think that it compleatly depends on the kid. Some kids can handle it, others can not.
I am pretty certain my parents felt I could handle playing some messed up games during the 90's, because they let me buy, or bought me, what ever game I wanted... I got Mortal Kombat 1 when I was about 13 I think.
It might be that they saw early that I was not negativly effected by stuff like that, since I was watching V (the original series from the mid 80's) when I was about 5-6, and a year or two later I saw the "A Nightmare on Elm Street" movie and "Friday the 13th", and other movies of that nature. Either that... or my parents did not give a shit (which might actually be closer to the truth XD ), and I just got lucky that I was never adversly effected by seeing stuff like that. XD
I grew pretty tired of horror movies by the mid 90's... so during the last 20 or so years I have felt that horror movies are extreamly boring. XD The only kinds I like are sci-fi horror stuff, and usually outerspace stuff... like Pandorum and simmilar movies... but I like those more due to that they are sci-fi then horror. XD
As far as I can remember I have never had a single nightmare in my life... heck even in dreams which feels like they are real, where I have been hunted by animals like bears or tigers, which I knew would eat me if they cought me, I was not scared. Heck I remember in the tiger one I flicked it on the nose one time to make it flinch, and then made my escape befor it took up the hunt again. XD
Not even after a dog bit me, in real life, on the inside of my right thigh (Waaaay to close to my junk, for comfort, like 2-3 cm below it) when I was about 6-7... not a single nightmare due to it. I was scared of dogs for a few years after, and the movie "Cujo" was a lot more scary to me then the other things i mentioned above that I saw back then. But that eventually went away and just turned into me having some respect for dogs and their capabilities, and knowing how you should and should not act around dogs.