At age 8 Critters. I couldn't go to the toilet alone for weeks after seeing once come out of the toilet. It's a PG too!
For reference I'd already watched exorcist by that age as my cousin and I snuck the copy out of my uncle's video shop. Exorcist didn't bother me anywhere near as much!
I never watched Ghoulies, but I'll never forget walking through the rental store and the box was eye-level with tiny kid me. Scarred me pretty bad. After that I was terrified of flushing the toilet, so toilet lid always had to be down and as soon as I flushed I would run from the bathroom.
Took me probably twenty years to completely get over it.