At what age must all men register for the Selective Service?

Men are required to register for the Selective Service when they turn 18 years old. This registration is an important part of the United States' preparedness for potential military conscription. By requiring registration at the age of 18, the system ensures that all eligible young men are accounted for in the event of a draft. It's a civic duty that aligns with the responsibilities of citizenship, particularly in the context of national defense and military service. Registration can occur anytime between the ages of 18 and 25, but the law mandates that individuals must register by their 18th birthday. The other age options do not align with this requirement, as they fall outside the legally established age range for registration.