I found a quote from a book that says of Ella Fitzgerald:

"The length of Fitzgerald's career is considerably impressive in the context of socio-cultural constructs during her era, and as a black female music artist, she claimed a wide range of nationally acclaimed accomplishments. Finally, despite the odds against her, "[Fitzgerald] was doubtless the longest singing career in American music, popular, jazz, concert, or any other kind of music, and it certainly is one of the most illustrious."

that may be hyperbole, but at nearly 60 years in major venues (started at 18, she sure is up in the list.