Earliest non-dos RPG game, that would have to be on consoles even earlier than the earliest computers (eg Apple II).
Not sure of this is accurate RPG 1979. That's the oldest according to that site.
A number RPG dos games could find their roots in earlier systems (even on Apple II, even before on Atari 8-bit and even before on earlier console and they were ported / remade to be better. The trick would probably to find out which console/computer is the oldest and find the RPG game. Then again maybe not.