2000 years ago? Less than 200 years ago the legal age of consent in many US states was 10 years of age. In Delaware it was 7. Recall that the laws of the United States were based largely on Judeo-Christian values.
In any case, 2000 years ago young brides were a matter not of ignorance but of a given people or tribe's demographic survival.
Trying to apply morality standards from today's societies to yesterday's is folly. Morality, especially in threatened or otherwise vulnerable societies develops in large part according to the functional needs of that society and what needs to be done in order to survive Child brides were a remnant of a time when infant mortality rates were almost the same as infant-survivor rates, and when overall lifespans were very short compared to today's standards. The survival of a society depended on its ability to keep its population at least stable and preferably growing so as to be able to fill agricultural labour needs as well as build strength in numbers to be able to ward off aggression from other neighbouring societies.
You could argue that in some parts of today's third and fourth worlds that this is still at issue even if only on small localized tribal levels, though clearly it is no longer so in any of the first or second world nations of today.