The Selective Service System is an independent agency of the United States government. It has information on those subject to the U.S. military draft. All male U.S. citizens and male immigrant non-citizens between ages 18 and 25 are required by law to register within 30 days of their 18th birthdays. They must also contact the Selective Service within ten days of any changes of any information they gave, like a change of address. Females, on the other hand, are not required to register.