Can you get married at the age of 12?
In some countries perhaps, but there are no US states which would allow someone as young as 12 to marry.
Roman girls were allowed to get married at the age of 12, but boys had to wait till they were 14.This was because people believed that a girl should get married when she reached the age of puberty, as then they would be able to give birth and the Roman believed that she would make a better wife. You had to be married by about 15-16 or you would be punished.
The legal age to get married without parental permission is 18 in the majority of the world. If you are underage, you can legally be married with permission from both parents, but there are limitations, most states won't allow someone under 16 to get married, even with parental permission. Some parts of the world, like Bangladesh, women are forced to marry and have children with older men at around age 12.