I read somewhere about the relationship between stress and the onset of menstration. It stated that in situations where girls are exposed to higher levels of stress or violence, that they begin having periods sooner. The study was a comparison of average age of onset of menstruation of girls in inner cities versus suburbs. The theory is that it has survival value for humans in general, such that during long periods of bad times the reproduction of the next generation can be speeded up, thereby increasing the population and subsequently the chance of survival. I would extrapolate on this and further postulate that violent entertainment could have some effect on these trends.
I never heard that, but it sounds plausible.