I remember the exact moment! I was 6 years old, at my grandma's house, playing with my cousins and running around, when suddenly we got tired and stopped in the living room. The TV was on, and episode 17 of Indigo League (Island of the Giant Pokemon) was playing. Even some of the adults were watching with us. It felt so surreal and unlike anything I'd ever seen, and just instantly caught my eye. It's the only episode in the anime (that I can remember) where the Pokemon talk, albeit via subtitles, and it only added to my amusement. It wasn't my first anime overall, but it came close (2nd).
When I got home that day, I instantly searched for more. I still don't really know what made little me love it so much, but I'm glad it did :)