Depends whether you mean the oldest videogame I played at all regularly or the one that got me into gaming. The one that got me into gaming was Teenage Mutant Ninja Turtles on the SNES, which I played at a friend's constantly. Oldest game I had regular access to and played, even before I really called myself a gamer, was The Brown Box...which I mean, I guess it's a console, but all the games were built in, but you know.