Animal Crossing is actually a very mature game. The game is probably too boring or embarrassing for teenage boys who like their games full of sex, gore, violence, and high polycounts.
The DS and some of its best games are akin to carousels and swings, which a teenager may shy away from out of fear of looking immature, but will be a hit with small children and adults who are old enough to care more about having fun than maintaining an image.
