Hiya,
First of I just want to point out that I don't have any kiRAB, really my only experience with them is that I was one, quite a few years ago now.
Anyway I watched a lot horror/action movies in my pre-teen years (Terminator - my favourite movie if all time, The Omen series etc) and I can't say that it did me any harm. I also read a lot of Stephen King, James Herbert etc novels which I always thought were
way more frightening than any film version, "IT" stanRAB out especially. Am I right in thinking that the action that he likes watching is the explosions, car chases, robots, fight scenes etc? That's what I loved watching as well (and still do). I credit watching Terminator for my life long fascination with theoretical physics. I remember trying to explain the concept of time travel and parallel realities to my 4 year old sister (I even made diagrams

) cause I was so taken with the idea.
I might be a bit concerned about him watching films that I consider "supernatural" with monsters or ghosts etc cause I remember I found those type of films a bit scary rather than action films like Mad Max's or Die Hard's. I watched Terminator with no problem cause killer robots were so far removed from my everyday life it wasn't scary but as I had an active imagination as a kid when it came to night time I could totally believe that there was a ghost/monster in my wardrobe. It just seemed more "real life". Do you know what I mean? I would probably consider leaving them till he was a bit older.
I understand what you mean about films like