I found a letter I wote for a class exercise when I was 12. It went into detail about how I needed to go on a diet. Again. I found that letter several years ago and it stll makes me so mad to think that any child of that age was already talking about dieting as if it were a normal thing- I was clearly not afraid of my teacher reading.
I do know I was conscious of weight at the age of 10. But it was a bit of an eye opener to actually have physical evidence of it.