At 21 he began working at the Bell Telephone accounting division and, before even graduating from law school, he was admitted to the Missouri bar. In 1913, he was married to Freda Josephine Prill of Kansas City. At age 24, Lynn took and passed the Missouri certified public accountant exam, earning the highest score on that exam ever made. Soon after, he began working for the largest underwriting insurance company in the country, U.S. Epperson, and quickly worked his way up in the company. By the age of 30, Lynn had taken out a significant and risky loan to buy the U.S. Epperson Underwriting Company. That step launched a successful business career that included insurance underwriting, oil well and orchard ownership, and large investments in the railroad business. He would become a prominent businessman in the Kansas City area as head of vast oil interests and as president of the world's largest reciprocal fire-insurance exchange.