Ethel Waters

Here she is, singing "Am I Blue," in 1929:

A 1925 recording of "I've Found A New Baby":

Here she is in 1975, almost 80 years old, singing "His Eye Is On The Sparrow" at some kind of revival meeting (as she explains, she got religion in the last years of her life):

...His Eye Is On The Sparrow is also the title of her autobiography.

Donald Bogle recently published a biography of Waters.  Read reviews here and here, and hear Bogle interviewed here.