The oldest system I own is an Atari 2600 Light Sixer from 1977 or '78, that sadly does not work properly.
My oldest game is most certainly an Atari game... Either Outlaw, Human Cannonball, Canyon Bomber, Bowling, or Space Invaders. They all came out around '77 - '79.
My second oldest system is a Mattel Intellivision from 1979.