Sorry for my wiseass reply before; feeling randy on a solitary friday night.
I'm at about 17, and you can see the outline of the pack, but none of the actual cans quite yet,if you see what I mean. They're about to break through, I think.
I'm American Japanese though, and I really strongly suspect that genetics has something to do with it. I knew some thin girls in Japan who had a relatively small amout of bf who still had no sixpacks. Because asians have relatively little booties (sad!) we can have no sixpacks at lower body fat. I seem to remember that Spatts who has a four pack at 37% bodyfat (I am so fucking jealous I could spit!) also has the ghetto booty thang going on. Like Phem said, it's all about where you hold your fat. I saw pics of Phem's abs I think, and she knows what the hell she's talking about!
Wyst