In general, as the single most explanatory rule of behavior “Do only that which you can pay the restitution for if you fail.” Because while unstated, it is the rule by which both legal, moral, and normative blame is determined.

They cannot pay and are not even cognizant of, the cost of restitution. And creating and bearing a child is perhaps the greatest crime moral crime, becasue it subjects family and indeed all of society, to moral hazard: they are forced to pay for your bad judgement, and the bad judgment of your parents and family, becasue they cannot morally correct your decision by killing the child. (Although that has been done frequently in history it is not done today.)

When the family was the principle unit of economic production, when we lived in intergenerational households because of it, when children began contributing to the work of the household by age five, when child mortality was as much as 50%, death in childbirth common, and the vicissitudes of life unpredictable, pregnancy uncontrollable, children disposable, and women in particular had no control over their destinies we treated children very close to domesticated animals. And none of those conditions apply today – at least, for anyone who would ask the question, or read the post.

For most of history 13–14 was the beginning of adulthood. Girls may be indeed mature enough to care for children by 16 and certainly 17 if they are under the care of an intergenerational household and began working in the household and caring for siblings from six or seven. Boys, if they are put to work by the same age, and have responsibility by 12 or 14, can be, like girls caretakers in an intergenerational household, especially if they have done any military service. But boys do not finish maturing until 22, just as girls are ending their optimum fertility (23). Our questionably effective education system has extended childhood development so much so that males are now mentally, emotionally, and socially mature only in their late twenties (if that). School is unquestionably effective through grade 5, but by grade 7 is only marginally effective. So we are effectively losing 5+ years of socialization, employment, and emotional development in order to keep children in school more than the entirely adequate 2–3 hours per day, if they participate in the work force in simple work after that (I started working holidays time at 7 years old. And by 10 and 11 worked holidays and whenever else I could. ) Under those conditions we could (as they do in eastern europe) have children earlier. Without those conditions, and perpetuating today’s environement, the single mother disaster will continue, and the boys that ‘check out of society and stay there’ will continue.

So the answer to age of sex at 13 is “Not in this current world we live in.”