The median age of a population is the age which divides a population into two groups of the same size, such that half the total population is younger than this age, and the other half older. It serves as a good measure of the overall age of the population because the more older individuals there are, the higher the median age will be and vice versa.

Switching between the different census years on this map, and viewing the comparative statistics in the table below, show how dramatically Pennsylvania's population has aged in the last few decades. It is not just a question of how much older it is but also of where in the state those changes are occuring.