oh so many... one of my best friends in school had divorced parents, and his mum would rent us literally any video at all, no questions asked. We had sleepovers where we watched all available Terminator movies, Alien(s) and many, many others at the age of about 11

Most of these were seen with friends or friends and their older siblings. We were all latchkey kids in the 80s, so there were few limits.

• Friday the 13th part 7
• Friday the 13th part 8
• Mad Max: Beyond Thunderdome
• Cherry 2000
• Mask - the Cher movie, not the cartoon I thought I was renting.
• Total Recall, in the theater, with a laissez-faire aunt who laughed at the triple chested character.
• To Wong Foo, Thanks for Everything, Julie Newmar - in hindsight, a great movie to have watched, but with no context it's bewildering for a 14 year old.
• Boys on the Side - same as To Wong Foo, the same weekend actually. Glad I saw it, wish I had any understanding of it at the time.
• Rocky Horror Picture Show - same as the above two, but when I was 8 or 9.

My parents were quite thoughtful about what we watched, but one of my earliest memories - around age 4, I think - is of terrifying movie being shown in some childcare setting I was in for a few hours. Teenagers got off a school bus, went exploring or hiking in some snowy, mountainous woods, and there was a white wolf (or several) that hunted them down. Pretty sure they died. At least they had to flee. I can still feel the fear! My poor parents were horrified when they came back to get my brother and I and found out what we'd been watching. I think it was White Wolves: A Cry in the Wild II, but I have zero desire to watch it to find out. 

Arachnophobia, when i was too young. That spawned years of irrational fear of spiders that i'm slowly getting over. 

When I was 9, my parents took me to see Midnight Cowboy at a drive in theatre.  They thought it was a western.

I don't remember anything about the movie, but I remember them leaving early and hurriedly driving out of the theatre. 

When I was 6 or 7, my parents took me to see the racing movie LeMans. This was about a year after we were in a head on collision in our VW van with a station wagon and the passenger in the other car went through the windshield, my dad's leg was crushed, mom was 8 months pregnant with my little brother and we three kids had a frightening ride to the hospital in an ambulance. We were all okay, but seeing the fiery wrecks in the movie was a bit traumatizing. I spent most of the movie backwards in my seat watching the projector. Still a racing fan, though.

My DAD of all people rented The Shining when I was maybe 9. Only halfway through and I noped out of the living room and probably locked my bedroom door that night. 

That video makes me reflect on how trauma isn't confined to the generation that survives it at the time; shout out to HBO's Watchmen short series for a propulsive grappling on this theme.

As for a movie that I saw too young, there were any number of horror movies like The Fog (I grew up in an area that got a lot of coastal fog), but the movie that was just far too graphic for my age (5ish) was the sci-fi movie Rollerball. I don't think any of my family knew I was watching from the hallway, but I was waaaaaay too young to understand anything other than how capricious the violence was.

So many.  Saw The Exorcist in the theater with my friend's mom when I was like 7 or 8. She took us to anything!

My dad took me to Rollerball in the mistaken belief that it was a basic sports movie and not incredibly violent

The 2 that really stick with me, are when I was about 9 I saw part of "Invasion of the Body Snatchers" (the '78 version with Donald Sutherland) when it was on TV at my aunt's house. I saw just enough to make me afraid to go to sleep with a plant anywhere close to my bed. Since then I've seen this movie probably a dozen times and it's one of my favorites.

Then a couple of years later, the father of a neighboring kid took us to see this 3D horror movie called "Parasite" (https://www.imdb.com/title/tt0084472/?ref_=nv_sr_srsg_3_tt_8_nm_0_in_0_q_parasite). I had never seen anything like it, and it gave me nightmares for weeks afterwards. I have not been tempted to see this one since.

Two stand out: "Poltergeist" when I was ten. I had the misfortune of a bedroom with a closet AND a giant tree outside my window. I don't think I really ever slept well until we moved out of that house about a year later. 19 years old: "Silence of the Lambs." I don't know what age would have prepared me for it, but 19 was not it. I'm still traumatized by that film, and I watched half of it balled up in my seat with eyes closed. I went with my housemate and he got a little container of ice cream at the concession stand. By the end of the movie, he'd chewed his plastic spoon flat into a spatula! 

I remember when I was young my parents went to the video rental store and came back with "The Little Mermaid", I was around 7, my sister was 4. However, the VHS tape that was in it was rather "Basic Instinct"...

They quickly realized and we didn't get very far...!  

Soooo many movies seen too soon. I was a precocious 1970's kid and my Mom and I were huge movie fans, going at least once a week, so naturally, just due to volume, there were a lot of things that were not remotely appropriate. Plus, that was then and they had a more feral parenting style. A couple of stand-outs:

1) "The Hunger", with Bowie, Deneuve and a very young Susan Serandon. My Mom took me to see it in the theater. I was 10. Probably could have waited on that one! Still love it!

2) "Prophecy" - Easily the best Eco-Horror movie IMO, but my Mom took me to see that in the theater at the ripe age of 7. We walked out, thankfully. Viewing it recently, it is comically terrible.

For me it was Poltergeist in the theater, I was 11. My parents took me... by the end, I was FREAKED, I recall being hot, lightheaded, nauseous. I was crying, no sobbing and my parents had to each carry me/walk me out with hooked elbows between the 3 of us. That physical experience was about as bad as being mentally freaked out as I was. Gawd.

The summer before I was in third grade, my father took me (us? I can't imagine I was the only sibling with him) to see The Godfather. I remember him saying years later how shocked he was that they were allowed to show that stuff (nudity, horse head) in the theater. I guess he wasn't old enough either. 

A few years later he took us to see Star Wars. He was soooo excited for us to see it on the big screen. Much more appropriate.

Watership Down, soooo much trauma

I too was forced to watch Platoon (as well as Hamburger Hill and Full Metal Jacket) before I turned 10. Dad was a Vietnam vet and has a powerful connection to the Marines so military movies and books were always around in our house. 

But the one that stays with me is the original IT. Never watched it again. Never need to. 

The ones i remember: Nosferatu (the 1922 one, during a party my parents were having it played on the TV, was certain vampires were real and it was a documentary at the time), The Elephant Man (age 11), Reds (age 12), Deathtrap (age 13), The Eagle Has Landed (probably 8?). I think my parents just took us to the theater when they wanted to see a movie and save some babysitting money.

Edit: Oh, I just remembered my cousins took us along to see Sharkey's Machine, man, that was messed up. And also Rollerball as someone above mentioned.

My parents never let us watch anything scary and neither did anyone else's parents, so I don't recall being particularly traumatized by anything. I vaguely remember being over at a relative's house and the adults were all watching The Day After but I don't think any of us kids were paying all that much attention to it.

I got the other kind of age-inappropriate showing: I was 9 when we went to see Kramer vs. Kramer over the holidays. For the physically disturbing aspect, I still wince at the thought of when Billy falls at the playground, and I looked away when re-watching the movie a few years back.

In other news, it would be 10 more years before my parents got divorced.

So many for me as well. Some I just watched thanks to some janky greeting-card-based un-scrambler thing for the cable box. Others because my dad wanted to see them and was fine with me enjoying them - I don't know how young I was when I saw The Deer Hunter the first time...

At my request, my older brother took me to see Silence of the Lambs for my 14th birthday.

'70s/'80s kid here! A sampling:

• Sleeper (age 3 -- I remember being terrified by the chase scenes but liking the giant vegetables; lord knows what I thought the Orgasmatron was all about)
• Elephant Man (age 11)
• Montenegro (age 12)
• Rollerball (age 14)
• the occasional soft-core porno on someone's parents' Playboy channel during a sleepover...

The Exorcist. I was 4 when it came out. And my Catholic mother took me along with her to see it. 

My folks would take us, in the station wagon, to double features at a drive-in. So, if you tried to stay up you might see a film intended for adults.  Two I remember - "Hell Is For Heroes" after "Mary Poppins",  and "Hud" after some Kurt Russel Disney thing.   I didn't manage to stay awake through either of those, however