One of the most outstanding examples of a late bloomer has to be Grandma Moses. Born Anna Mary Robertson on September 7, 1860, she was interested in artistic activities from the time she was quite young. As a child, she used unusual materials: lemon juice and grape juice to paint landscapes, ground ochre, grass, flour paste, slack lime and sawdust.
Although Anna Mary Robertson Moses (she married Thomas Salmon Moses when she was 27) was creative throughout her life, she didn't start her prolific career until, at the suggestion of her sister Celestia, she turned to painting at age 76 when her arthritis made it too painful to embroider. A few years later, a collector happened to see some of her work, bought everything she had on display in a local drugstore and, in 1940, arranged for a one-woman exhibition of her work at the Galerie St. Etienne. Her fame grew until she was known internationally, and she continued painting for the rest of her life.
For more about Grandma Moses, check out these websites:
The Biography.com website (Published by A&E Television Networks)
New York Times Special (Biographical Obituary)
Galerie St. Etienne (Biography and Chronology)
Grandma Moses in the 21st Century (Presentation by the Orlando Museum of Art)
National Museum of Women in the Arts (Artist Profile)
Grandma Moses on Artsy (Brief Bio, Images of Her Work)
Wikipedia (of course)