Uh... 5, I think? I can't remember exactly when we got Population Growing but I know I was pretty little. I know I got Wild World a while after it came out, so we stuck with the GameCube one for a long time.
4, maybe 5. I was playing the GC version all day every day! From the moment I woke up to the moment I fell asleep. While my siblings went to school... they were so jelly.
I think I was around 13 when I first played Wild World, and after that I was hooked on the series. My mom got it for me for Christmas, thinking it was a city builder like game (I used to play a lot of those as a kid so I had a lot of them) but one where I also had to take care of animals. She was kinda right.