Wolfenstein 3D. I played it when I was 4 and oddly enough it was one of the earliest memories I still remember, since 4 was when I started remembering things I guess. It wasn't when it was first released, this was in 1994. I walked in on my mum playing her brand new copy of Doom II (I remember her zooming in the door of the house and immediately to the computer room. Hah, I love having a gamer mother.) and she was like "nooo you aren't old enough for this game" and threw me out of the room, but she figured that Wolfenstein wasn't nearly as bad as Doom and since I seemed interested in a shooter type game she let me try Wolfenstein 3D, though she watched me and made sure I didn't turn into a homicidal psychopath. I didn't.