As I understand it, until the industrial revolution, we had children and adults, we didn't have this special in-between time called the teens. Life was shorter and adulthood began early. Old enough to reproduce = adult. There have pretty much always been taboos on intercourse with those not old enough to reproduce.

Not very. It was seen as unseemly to marry off your daughter before she was ready to be a mother. To have her engaged and betrothed is another story. There are lots of stories of marriages arranged at birth especially in wealthy families. That doesn't mean that they happened. They were just neggosiations. And due to the fact that women began their cycles later preteen births were more then uncommon they were unheard of. You can't be a mother without puberty which didn't start till around 15 or 16. Not to mention that girls were kept under lock and key from the time they were about ten on. And if they did become pregnant the chance that they would die before or during childbirth was astronomical. It's actually become more common as time goes on. But no less dangerous.

I think in some cultures it was very common. I don't think it was ever common in my present culture.

I don't know how common preteen marriages were but childbirth at such a young age was probably very rare. Girls need to have a certain level of body fat and nutrition to be able to go into puberty and until very recent modern times girls in their preteens just were not capable of having children. More than likely they were older than girls today when they became able to bare children.

There's not a clearly defined mathematical curve for this. The standard age of marriage has fluctuated in various ages and various cultures. Even within a single culture, marriage practices between the nobility and the peasantry might be vastly different. In Renaissance Italy, it was not uncommon for noble girls to marry around age 14, but peasant girls were more likely to marry around 17 or 18. A betrothal might be arranged long in advance of that age and even the marriage ceremony might be performed before one or either party reached puberty, but such occurrences were usually driven by politics. The "consummation" of the marriage would not take place until puberty.

When I was a young girl, my friend, an Armenian, introduced me to her mother, who had married at age 12. This was not uncommon. In the past, people married much earlier. There were no other options. Even today, children as young as 8 or 9 are marrying. It is considered inviting trouble to have a pubescent girl around the house, unmarried, who might get pregnant out of wedlock. So marriages take place as soon as puberty is reached. It is only in industrialised societies that this has largely changed. In these societies, women are educated, and can work, giving them other options than an early marriage.

preeteen marriges were commin julliet in shakespears play is ment to be 12 herself

Preteen marriages were never common in the Western World (Greece, Rome, Medieval Europe, or even among the Semitic peoples of the Near East). They did happen, of course, though usually only among royalty and nobility, and the marriages weren't consumated until much later: e.g., Julius Caesar and his first wife were married at 10 and 7 respectively - his uncle Gaius Marius had made him Priest of Jupiter (Flamen Dialis) for which he had to married - but the wife was raised as his sister, and the marriage wasn't consumated for another 10 years. (She bore him one daughter, Julia, and then died in childbirth along with their son 2 years later.) Nobles and wealthy merchants of the Rennaisance might marry off their 13-15 year old daughter to a wealthy man, typically much older than 20, but this was not the norm for most people. The major inhibitor was attitudes about wealth and self-sufficiency. Especially in Western Europe, a man did not marry until he could provide for a wife and children on his own, usually signified by having his own house. Apart from political and business alliances of the mighty and wealthy, men typically didn't want a child-bride, but a woman who was mature and robust enough to handle the arduous task of keeping house and bearing and raising children, so 17-18 was about the minimum for them -- but then he might have to keep the girl waiting for many years until he could afford to marry, and older men prefer women in their early to late 20s, not teens. The fact is that the average age of marriage actually fell in England by more than 10 years between 1750 and 1850: increased prosperity due to the industrial revolution meant that men could get married at 20 instead of 30, and the result was about 3-5 more children per family and the resulting population explosion. Ancient, but long standing, Arab and Semitic law set the age of the bride as Half the Groom's age plus 7 years: he's 20, she's 17; he's 40, she's 27. India and the areas most effected by Indian civilization seems to be the only place where marriage between 2 prebuscents was common (Gandhi and his wife were 11 and 10 on their wedding day, as I recall), but again, these would not be consumated until they had reached puberty. What can be confusing for modern folks, however, is the practice of betrothal, which was as legally binding as marriage, and in fact was usually described and treated as such: once betrothed, you were virtually married: the boy was a husband, the girl was his wife, but they didn't live together or have conjugal relations (typically) until the actual wedding, which could be years away. Typically, cultures where most girls are married off and impregnated as soon as they reach child-bearing age are those that have an extremely high child-mortality rate, and low life-expectancy. Other cultures where it's normative tend to have an excessive fear of unmarried girls losing their virginity -- or more commonly, the fear that others will think them promiscuous and "damaged goods" just because they're past puberty and unmarried.

I honestly believe it was more common in ancient times then it is now. Back then parents chose who their kids were to marry.