Unfortunately, my Nintendo 64 recently kicked the bucket, so my oldest system would be my GameBoy Advanced. It's a see-thru teal color, and I broke the battery compartment cover some time back when, so I have to hold it on w/tape. I do have my old 'brick' Gameboy, but it doesn't work, so I'm not gonna count it. Also have my Gameboy SP. It's one of my favorites. It's black and has 'Who are you?' graffitied on the 'top'.(not by me, I bought it like that)Works just fine. I love holding it, it's just so wittle and cute compared to my big'ol 3ds XL. ^_^
And I'd have to say that the oldest game I have is either my Pokemon Yellow or Asteroids. Asteroids would probably be older, though I'm not 100% sure.