I think it might be Pokemon Yellow.

I think I have a copy of the CD version of System Shock 2 lying around somewhere.

The oldest game I still have would be Ultima IV followed by Red Storm Rising, both in 13.3cm disk format for the C64. I'd have older but my atari got thrown out some years ago

In my apartment? King's Quest VI.

At my parents house? Hard to say, because we had two or three boxes full of games on 5 1/4 floppy. We had games like Leisure Suit Larry, Test Drive, etc all there. I think the oldest I can remember is One on One: Larry Bird vs. Julius Erving, which I could NEVER figure out how to play.

The oldest game I have now is either Vampire the Masquerade: Bloodlines or Arcanum.

Here in my place the oldest is probably Skullmonkeys for PS1. Bought in 1997

Warlords for the atari

i believe 1983 or something