Younger males do risky things because that's when they're looking for mates. Death rates start to spike for males in their teens and then decline in their mid twenties, whereas the lines for females smoothly increase as they age.

That aside, if you do a regression on the incidence of murder rates, both age and marriage status are significant. So yes, age explains some of it. So does marriage status, independently.

Regardless of the reason that marriage keeps you out of violent situations, the point still stands that being unmarried is a risk factor for violence.

You should remember that there is already a selection process going. Most women will refrain from marrying a violent person. The violent person will therefore be "unmarried" yet the high crime rate hasn't anything to do with marraige.

Then why do so many females like Twilight?

Both the risk and potential payoff are far greater for male then female. A woman can hope to have around 5-6 surviving children, with little risk to have none. A male has a real risk of dieing without children, but on the other hand the best case scenario is in the hundreds of offspring.

But the real consequence of a bigger male-to-female ratio will probably be plain old fashioned competition. Some men, especially young, will go the "flashy" way, but for most it will simply mean that having outstanding performance in whatever they do is much more important. Wouldn't want to be one of them, but for the society as a whole is probably good.