Population aging is a process that is gradually developed between individuals and the community. Under a demographic perspective, aging is a consequence of several factors associated with mortality and fertility evolution. This paper analyzes demographic tendencies and changes in age structure in Mexico by federal state. We are pointing out the plausibility of overestimation of the population in advanced ages. Special emphasis covers application of a modified Whipple index. The data used derives from the Mexican population censuses 1970 a 2000. The results obtained show errors in the declaration of ages in such population, as well as the inconsistency between the proportion of the population and the stage of demographic transition in some Mexican states.