When we say "ancient Mexico" we refer to all cultures and historical processes that took place in the territory now occupied by Mexico before the Spanish Conquest. When we use the term "Mesoamerica" we speak exclusively of the southern half of Mexico and its coasts. Mesoamerica is the large area in which civilization developed; while Northern cultures maintained a more rustic way of life and most of them did not practice agriculture.
There are signs of human presence in the territory of what is now Mexico by the year 24000 BCE, during the ice age. The oldest known skeleton belongs to The Woman of Tepexpan, a hunter from 8000 BCE crushed to death by a mammoth in the mire of the shores of Texcoco Lake. Shortly thereafter the large animals from the Pleistocene would disappear and the recollection of fruits and seeds that led to the development of agriculture would intensify.
Around 2500 BCE there were permanent villages with adobe buildings in which pottery was made. We believe that the history of Mesoamerican civilization begins on that date.