I think I started playing around 2004 when I was 8, I'm 16 now. Also I don't think you must be over 20 to fully experience the game. This game was the game that made me realize how much I loved animals and also how ADD a lot of people were around me.
I was 10, I think, when my sister and I got AC:WW. I'm 16 now.
It was the first DS game we ever played, so it's very special to us. The game was incredibly magical (~magical~) to us back then, as we didn't know any game like that even existed. No other game compares! AC has become a great way for us to bond.