Selective Service System | 1,693 followers on LinkedIn. An independent federal agency & our nation's best insurance policy. All men 18-25 need to register. www.sss.gov/privacy/ | Our mission is to register men and maintain a system that, when authorized by the President and Congress, rapidly provides personnel in a fair and equitable manner while managing an alternative service program for conscientious objectors. Virtually all men - ages 18 through 25 - must register at sss.gov. The obligation of a man to register is imposed by the Military Selective Service Act, which establishes and governs the operations of the Selective Service System.