When must all men register for the Selective Service?

All men are required to register for the Selective Service upon turning eighteen years old. This requirement is part of the United States' system for maintaining a reserve of personnel that can be called upon in the event of a national emergency. The age of eighteen is significant as it marks the transition into adulthood when individuals are eligible for various responsibilities, including military service. This regulation ensures that eligible young men are accounted for, facilitating the government's ability to mobilize forces if necessary.

The other ages listed do not align with this legal requirement. For instance, twenty-one is considered the age of majority for drinking alcohol in many states, but the obligation for Selective Service registration occurs at eighteen. Similarly, while seasoned in contexts like education or parental obligations, sixteen and seventeen are not the legal registration ages either; individuals at these ages are still under the legal adult status in the U.S.