Yeah, I believe the first game that I officially finished was Pokemon Blue, with Pokemon Yellow following after that. Let me tell you, it was quite the tricky experience trying to finish the rest of the games that I played... For one thing, I was kind of bad at Super Mario Bros. Well, 'bad' as in, I couldn't get the timing of Mario's jumps down perfectly, and it always ended up with me bumping me against a goomba or something. Or falling to my death. The Legend of Zelda for NES had a really big over world, so, I of course was lost in Hyrule constantly, ahaha. Which was a really bad thing too, because there were places where you'd be 'in the wrooong neighborhood' so to speak, so, the enemies are way to tough w/ your lack of hearts and items.
I believe I was 9 years old when I beat Pokemon Blue, where I started to fully understand some of the mechanics of pokemon Blue, like, raising pokemon other than your pokemon starter, and actually using type match-ups to your advantage. Squirtle saved me a lot of grief in the Rock Tunnel, for example, ahaha. Hm, after I beat Pokemon Yellow, I tried my hand at beat the N64 games, which included Star Fox 64, Kirby 64, Mario 64, and the Ocarina of Time. I finally beat them when I was 12 or so, but it was quite the experience!