How old was Clara Barton when she started helping the wounded soldiers?

Civil War nurse Clara Barton founded the American Red Cross. Barton was a teacher and a U.S. Patent Office clerk before devoting herself to nursing in the American Civil War (1861-65). She earned the nickname "the angel of the battlefield" and in 1864 was named superintendent of all Union nurses. In the 1870s, officials of the International Red Cross invited her to help form a branch of the service in the U.S.; she agreed, and led the American Red Cross for its first 26 years.

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If you use those dates so would have started her career at 40