The average life expectancy was mostly cut down by infant and child mortality due to starvation and illness, but if you got past the early years where you were fragile to disease and hunger, you could survive easily into old age, especially if you were wealthy enough to afford care in your later years.
Also, children were expected to take on adult responsibilities as early as they were able to carry them out.
Females are a resource, a resource with unique value to males as a source of pleasure (sexual and otherwise), and with a value to their genes as a means of producing more organisms that carry copies of themselves in them.
Females can provide other uses in addition to those, such as labor and companionship, but so could other males.
When it comes to the "adult" responsibility of sex, all it takes from the female is just to be present, the male will find a way to use her body to make his genitals feel good so that his semen comes out. She is capable of this from the time she is born.
Therefore the limiting factor is to her survivability, which depends on her, but also on what the male does with her, some acts will "break" her (kill her or leave her unable to produce children), and the males who use their females for these acts will be left unable to use her for the purpose of passing on copies of their genes, this would include genes for behaviors, such as the ones that led to the deaths of their females, thus these males are likely to die out over successive generations with high rates of reproductive failure for the males that possess these behavioral traits.
However, this is not the only factor to consider, what should also be taken into account is that for the reasons listed above, females who are left some for some period of time are more likely to survive, and this reflects upon the behavioral traits of her close male relatives, particularly their fathers, who, being the first males to encounter them, would be the first to possess, and therefore take ownership of them.
This means that males with genes that instill some degree of protectiveness over their daughters would be better at passing their genetics to a third generation than those who do not.
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