Not sure that it's something to worry about. My parents were really permissive about gore and violence when I was growing up. I watched R-rated films from my earliest years, and it didn't affect me much (Predator gave me a tree phobia when I was four, though.
) I was obsessed with fighter plane video games at your son's age, and that didn't affect me, either. If your kid isn't aggressive (or showing signs of developing aggression), I wouldn't worry about it. Just reasonably limit his consumption and maybe look for other channels to satisfy his gore-obsession, which I have to say is pretty typical for boys. Maybe give him some surgery simulators.
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I have not the kind affections of a pigeon. - Ralph Waldo Emerson