re: average age of marriage
The average age of marriage for women during much of the middle ages was in the early twenties, and older for men. That's for the average person, not some member of the royalty that had an alliance marriage made for him/her when they were children, usually by proxy and certainly not consummated until they were of age. The reason for the commoners needing to wait: they needing to actually learn how to do a job, even if that was farming. Mommy and Daddy peasant weren't going to be able to set them up, so they needed to actually have earned some money to have an independent life.