Pokemon was my first, I was 4 or 5 at the time. I was in an afterschool program when someone brought a video with the first couple of episodes, and it was instant magic. I remember buying the games as well. It wasn't until around the third film when I finally lost interest, although I still act like I'm a big pokemon fan. I still play a bit of the games, but I don't watch the show anymore because from what I saw of the newer shows it looks like shit.
Ranma 1/2 was my first manga when I was 10. I found volume 15 in a local library and got hooked, and started buying almost every other volume at Borders, and I've only seen a couple of episodes of the anime (The "For The Love of Akane" volume was the first anime DVD I bought). I finally stopped when I was buying more volumes at a different Borders and got ratted out by the cashier because it was intended for an older audience, and my parents scolded me, even though at the time I was already watching some even more objective stuff like Wolf's Rain and Cowboy Bebop. When I got older they stopped caring, but I never got around to buying anymore. Now and then I'd re-read some of my volumes, though, and I'd still enjoy them.
Since then, I started watching stuff like Digimon, Yugioh, and later the Toonami and Adult Swim stuff like DBZ, FLCL, Inuyasha, and Fullmetal Alchemist. I'd even finding anime outside TV, like Fushigi Yuugi. Then when I got internet connection I started watching stuff like Death Note, Haruhi, Higurashi, Elfen Lied, etc.