Part of me wants to say Galaga or Pacman just because my mom was obsessed with those. I wouldn't be surprised if I started out with some arcade classic like those.
However, my family has always had a good number of consoles. When I was 1 or 2 years old, we had an Atari 7800, NES, Genesis, Turbografx-16, SNES... I think that's it. I played all of those systems all the time.