Most places in Mexico now require a university-level degree Licenciatura, BS, Maestria, Masters, etc) plus an ESL or EFL certificate (minimum) .. to teach English at the University level and many language institutes. Just being a Native Speaker with an interest to teach (regardless of teaching credentials or experience) is no longer an employable condition of preference.
You will not find jobs in public/State schools or universities because all hiring is controlled by union lists, which require you to have citizenship status in Mexico. Also, due to its proximity to the USA, there exists an oversaturated supply of Mexican speakers of English. Most language departments in both Institutes and Universities are staffed by native Mexicans.
Your age is also a limiting factor for serious institutions. You might try the peace corps. Many institutions look for additional help during the summer to help with summer language programs for children. You might try something like this to start .. problem is that the Summer is drawing to a close soon.
If you want to teach English, I recommend selecting a different country with higher demand for Native Speakers and better salaries. The most that you would make in Mexico as a starting teacher is about $300 per month, enough to cover rent only.
If still interested in teaching in Mexico, you should try to get a Cambridge-level English teaching certification first. It will open some doors and show that you are serious about teaching English.