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.
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.