When must all male citizens register for the Selective Service?

All male citizens are required to register for the Selective Service at the age of 18, as mandated by U.S. law. This registration is a crucial step in the event of a national emergency where the government may need to draft individuals into military service. It is designed to ensure that the country has a ready pool of individuals who can be mobilized if necessary. The age of 18 is selected because it aligns with the age of legal adulthood in the U.S., at which individuals gain full civic responsibilities and rights, including the ability to vote.

This process is not applicable to males under the age of 18 or those above the age of 25, which distinguishes it from other age-related regulations, such as voting or drinking age. Thus, the requirement for registration at age 18 is a key element of civic responsibility for male citizens in the United States.