The issue here is that people are going for the lower common denominator (the threshold of child molestation) and using it as an analogy for age of consent (which is 18 in most states the lowest states being around 16, which is normal for continental europe).
Age of consent, which lets define as the age at which every individual is considered a fully independent adult is 16-18 in Mexico.
The whole 12 years old is the part of the law in which there is absolutely no room and is considered rape, a 12 years old fucking an 11 years old is automatically going to be considered rape, a 13 years old fucking a 12 years old isnt automatically going to be considered rape.
The cultural age of consent, which was the age at which it was normal for girls to be open for marriage is 15 years old and its celebrated in the "quinceañera". Any grown ass man fucking teenagers (even legal 18-19) is still considered a creep.
The whole rape is culturally seen as ok in Mexico its a fucking joke. The closest you get to that is in backwater towns controlled by indians with some autonomy where other laws tend to apply and where people make their own laws.
For example in these backwater towns if you rape a girl you need to pay up some "blood money" to get off the crime, but if state or federal level authorities get word of it they will most likely act, but for the most part they leave them be.