I have no idea, all I know is that my parents didn't give a shit if I played or watched something violent. However, they would send me off to bed if a movie had sex scenes. WTF?
But, yeah, I mean N64 came out when I was in grade 5 or 6, and I had Turok 2 for that which was probably one of the most gory games for that age. Oh and renting Resident Evil on the N64 (RE2?) was pretty awesome. I also played Blakestone, Wolfenstein 3D, Doom, Doom II, Quake, and Duke Nukem 3D when they were new. I don't know if they had ratings back then but I'm fairly sure they would have got "M"s. That would put at around 7 years old. Maybe 8.