How do you even get cavities, man. I've never had one, and I was a complete swine as a child. Went weeks without brushing sometimes.
I only started brushing my teeth regularly around high school, as I quickly realized foul breath can be a hindrance to socialization. But my teeth were always fine, never even got plaque or anything.
On the other hand, I pretty much always floss after eating, but that's because I can feel the bits of food stuck between my teeth and it's really bothersome. I don't understand how would someone not floss, actually.