Alien when I was about 10
This. Trouble is when you get older you realise how films are made, and they stop being scary.
You realise which characters will stay alive, and which won't. You understand that Hollywood demands a happy ending in all but the most extreme cases. You know that the main characters will be saved no matter how desperate the situation appears.
In short, films stop being scary.
However - I should note that I spend my early childhood reading Stephen King and other horror authors. I scared myself stupid as a kid reading books until midnight, then having nightmares about them.
After that, nothing fictitious scares me. I'm very scared about things that happen in real life, however




