I find that most horror movies from the 70’s/80’s don’t hold up. When I watch them now the special effects are just too hokey and ruin my suspension of disbelief too much for the movie to still be scary (or even particularly enjoyable). That is not true for Alien. It’s one of the few horror movies of that era that is still as intense today as the day it was released (The Exorcist is the other movie on that list).
My 13 year old son is currently “Alien curious”. I’m not rushing him into it, but I don’t think I’ll ask him wait until he’s 18 either. I can’t remember how old I was when I first saw it, but it was definitely younger than 18.
The last time I watched it was probably 15 years ago…in a theater…with Tom Skerritt in attendance.