AGE OF MAJORITY
As said in the introduction, we can go far into the past to see the progress made regarding the concept of age of majority. The age of majority is conceptually defined as the age when one becomes an adult. Age of majority may vary between countries, but legal implications are equally important: the capacity to contract, to exercise political rights, to become subject of adult criminal punishment, etc.
Let me start by saying that the age of majority is not a Western-only concept. In Mexico, the code of Nezahualcoyotl (1427-1472) stated that children under the age of 10 could not be held responsible for a crime (Soto 2007). The majority of age in Aztec times was 15 years old. For today’s standards, penalties under the Aztec rule were extremely severe, including for minors. Minors between the ages of 10 and 14 could be held responsible for a crime and punished by death, slavery, confiscation of property, and/or exile (Gutierrez 2008). However, it is said that punishment for minors was more lenient in comparison to adults, with two exceptions: crimes of insults against parents or parricide, where the penalty was death, irrespective of age (Gutierrez 2008). This clearly shows that family as an institution was more important than the concept of childhood for the Aztec. Later on, at the age of 15, youngsters would become adults and had to leave home for the Calmecac4 or the Tepuchcalli in order to receive religious, military, and civil instruction (Soto 2007). It must be said that these schools had a court of their own with a judge and its own procedures to assure justice among their students.
During colonial times, the Legislacion de Indias of 1680 fixed the age of majority at 18. It stated that those under the age of 10 could not be punished for a crime as they could not be held responsible for their behaviors. Between the ages of 10 and 17, minors could be held responsible. But the death penalty could not be applied to them in any case. These legal terms were based on the Siete Partidas of Alfonso X, which also stated that children under 10 could not be found guilty 
of any crime, yet those between the ages of 10 and 17 could be punished to some degree for most crimes, although not for all (e.g., minors under 14 could not be found guilty of sexual crimes).
The year 1841 marks the date of the first true Mexican criminal justice legislation with references to minors. It was called Ley de Montes. It established the age of majority at 18 years old. It also stated that minors below the age of 10 could not be held responsible for a crime and that those between the ages of 10 and 17 could be prosecuted and sanctioned. It did not bring major changes, but it was the first Mexican legal document referring to the legal status and age of majority of juveniles.
The criminal code of 1871 was an example of modernity and progress. It established that children under 9 years old would be exempt of criminal responsibility (Cruz 2007). The responsibility of those between 9 and under 14 would be decided upon expert opinion, while those between 14 and under 18 could be held responsible for a crime (Cruz 2007). In all cases, convicted juveniles would have to be held in a correctional center for the time of their sentence and until they had finished their primary education.
The 1928 Law for the Social Prevention of Child Delinquency in the Federal District and the Territories, also called the Villa-Michel law, established that minors under 15 could not be judged according to the criminal code. The age of majority remained at 18, but minors under 15 years were not to be prosecuted nor convicted by police and courts for adults. They were sent to specialized courts for juveniles. In 1929, the institution of Court Judge for Minors was created.
Today, the 2005 constitutional reform of article 18 homologated across all Mexican states (32) the age of majority as 18 years old. Only minors between the ages of 12 and 17 can be held responsible for a crime. No minor under the age of 12 can be held responsible for a crime in Mexico; however if they committed a crime, they will have to be rehabilitated and provided with guidance. Internment can only be applied to minors over 14 and only for violent crimes.