Languages are only as old as the generation that currently speaks them. There are no such things as prehistoric languages still being spoken today, they died out with the people who spoke them, and it is the language that they passed on to their children, and their children's children that eventually survives in the languages of today. Between two generations, the differences are usually minimal, but...they can be quite large. Grandchildren usually have quite different ways of speaking than their grandparents, these are the signs of language change. These changes can affect every aspect of a language. One of the most obvious of these is the lexicon, or the words we use.
Lawrence A. Reid, "Who are the Indigenous? Origins and Transformations," p. 7 (paper read during the 1st International Conference on Cordillera Studies, 08 February 2008.