57. the answer is...

at age eighteen (18)
between eighteen (18) and twenty-six (26)

President Lincoln tried to draft men to fight during the Civil War, but many people became angry and rioted. In 1917, Congress passed the Selective Service Act. This act gave President Woodrow Wilson the power to temporarily increase the U.S. military during World War I. In 1940, President Franklin Roosevelt signed the Selective Training and Service Act, which created the first draft during peacetime. This was the beginning of the Selective Service System in the United States today. The draft was needed again for the Korean and Vietnam Wars. Today, there is no draft, but all men between 18 and 26 years old must register with the Selective Service System. When a man registers, he tells the government that he is available to serve in the U.S. Armed Forces. He can register at a United States post office or on the Internet. To register for Selective Service on the Internet, visit the Selective Service website at http://www.sss.gov.