Background: Norman Percevel Rockwell (February 3, 1894 - November 8, 1978) was a 20th-century American author, painter and illustrator. His works have a broad popular appeal in the United States for their reflection of American culture. Rockwell is most famous for the cover illustrations of everyday life he created for The Saturday Evening Post magazine over nearly five decades. Among the best-known of Rockwell's works are the Willie Gillis series, Rosie the Riveter, The Problem
Context: Norman Rockwell was born on February 3, 1894, in New York City, to Jarvis Waring Rockwell and Anne Mary "Nancy" Rockwell, born Hill. His earliest American ancestor was John Rockwell (1588-1662), from Somerset, England, who immigrated to colonial North America, probably in 1635, aboard the ship Hopewell and became one of the first settlers of Windsor, Connecticut. He had one brother, Jarvis Waring Rockwell, Jr., older by a year and a half. Jarvis Waring, Sr., was the manager of the New York office of a Philadelphia textile firm, George Wood, Sons & Company, where he spent his entire career.  Rockwell transferred from high school to the Chase Art School at the age of 14. He then went on to the National Academy of Design and finally to the Art Students League. There, he was taught by Thomas Fogarty, George Bridgman, and Frank Vincent DuMond; his early works were produced for St. Nicholas Magazine, the Boy Scouts of America (BSA) publication Boys' Life, and other youth publications. As a student, Rockwell was given small jobs of minor importance. His first major breakthrough came at age 18 with his first book illustration for Carl H. Claudy's Tell Me Why: Stories about Mother Nature.  After that, Rockwell was hired as a staff artist for Boys' Life magazine. In this role, he received 50 dollars' compensation each month for one completed cover and a set of story illustrations. It is said to have been his first paying job as an artist. At 19, he became the art editor for Boys' Life, published by the Boy Scouts of America. He held the job for three years, during which he painted several covers, beginning with his first published magazine cover, Scout at Ship's Wheel, which appeared on the Boys' Life September edition.
Question: When did he have his first work published?

Answer:
age 18