Seeing some guy get folded in half in Disney's movie The Rocketeer was traumatic enough for me, and I was ~13. Not to mention melting the shoe in Who Framed Roger Rabbit.

It's hard to tell what will or won't deeply affect a child and even harder to gauge the specific ages where things might become appropriate. It's really per-child, and no matter how well a parent does gauging that, mistakes will be made.

There's no way this can be automated, as it's never going to be one-size-fits-all. The combination of generally sanitized media channel + parental supervision will (and should) endure, IMO.

Yeah, I was 8 when I saw Roger Rabbit, and it was the right level of scary for me, but a lot of my friends were really spooked by it.