Aztec education was heavily focused on two aspects: the religious and the military. The Mendocino Codex depicts how the Aztec youth were instructed from their birth.

When an infant was born, the midwife or Tecitl would give a speech that remarked on the social function and distinction between men and women. Before the baby could walk there was a special ceremony in which the parents would "consecrate" the child to his/her future school. A lot of the education was give at home and it was expected of the parents to teach children the social norms and important customs. It was a harsh education and punishment was clearly delineated:

3 yo would get verbal reprimands 4 yo physical punishment 8 yo threats of punishment by maguey barbs 9 yo punishment by maguey barbs 10 yo boys would receive caning and girls would be tied and threatened with caning 11 yo punishment by chili smoke 12 yo boys slept in wet ground. girls were made to sweep the streets after dark

Girls were expected to learn to pick and spin cotton, sewing, grind chili, sweep and clean the house among other house chores.

Boys were taught to farm, trade, make fires, mend fishing nets and fishing. Often they would also learn their father´s trade.

Among the social norms that were taught were: love and obedience to their parents, fear of the gods and duty,

Public education began at 15 yo. Depending on the social class of the student they could either go to the Calmecac or Tepuchcalli.

The Calmecac was reserved for the noble classes. The school was located next to the temple and the noble class could study to become a priest. There were 3 grades each 5 year long. Besides the religious education they received martial/military education. There were some science classes which included astronomy and calendar reading, public speaking, writing and math. Some women were admitted to the Calmecac but they were only taught the religious aspects.

In the Tepuchcalli was for the rest of the population. There was one in each part of the city. They had to keep the school and work for it`s maintenance. They also help building streets and temples for the city. The main focus of this school was war. They learned survival skills, fighting with diverse weapons and spying. Women were allowed to an all female Tepuchcalli they were taught domestic chores and religion.

TL;DR: at 12 you´re still being educated by your family in the basic social and whatever trade your family has.

Sources: 1.- CLAVIJERO S.J. Francisco Javier: Historia Antigua de México, Ed. Porrúa, Colección "Sepan Cuantos..." no. 29. Apud LEON PORTILLA: La Filosofia.., cap. V. p. 222.

2 .- SOUSTELLE Jacques: La Vie quotidiènne des Aztèquez a la veille de la Conquête Espagnole, Ed. Hachette, Paris 1955, p. 203.

3.- Larroyo Francisco, Historia Comparada de la educación en México, 1947 pp 29-33

5.- Florentine Codex, part. IV, translated from Aztec into English by A.J.O. Anderson and Ch. E. Dibble. Apud LEON PORTILLA: Filosofía..., cap. V, p. 225.