I actually found the full text of that journal article about the relationship between fruit and vegetable intake and breast cancer:
JAMA -- Consumption of Vegetables and Fruits and Risk of Breast Cancer, January 12, 2005, van Gils et al. 293 (2): 183
It is almost disturbing. It seems like a no-brainer that a higher intake would lead to a lower risk, but that isn't what they concluded. Maybe the biggest thing is just not having
no intake. I don't know, I wish someone could explain this to me.
Also I wanted to comment on your question 'Why are only grown-ups the most affected?' Now, I'm no expert by any means, but I have read a bit about genetics. I think the reason is that as our cells divide, they have a tendency to mutate and mutations cause cancer. As the genetic data keeps getting passed around, like a game of telephone, it gets more and more unstable, so the older you are, the more likely you are to have these harmful mutations. One of the most interesting things that I have read about is the Telomere, which from what I understand, simply acts a buffer in the DNA. It was explained as the border around a sheet of paper. If you put that paper through a copy machine, sometimes the copies are misaligned. The border, which is useless whitespace, acts as the buffer. It also has something to do with cancer, but I don't know enough to explain it:
Telomere