This slide depicts the number of people in the U.S. population of retirement age (light gray: 65 and above; dark gray: 85 and above).

In the early 1900s, the U.S.A. was populated by a relatively small number of older people.  This situation changed drastically after 1920:

    # of U.S. residents aged 65 or older

   1900   3.1 million people
   1920   4.9 million people
   1940   9 million people
   1960   16.7 million people
   1980   25.7 million people
   1990   31.2 million people
   2000   35 million people