Mark Twain at 15.

Samuel Langhorne Clemens, later known as Mark Twain,
was born in Florida, Missouri, on November 30, 1835.

Clemens was apprenticed to a printer at age 13 and later
worked for his older brother, who established the Hannibal
Journal. In 1857, the Keokuk Daily Post commissioned him
to write a series of comic travel letters, but after writing five
he decided to become a steamboat captain instead.