https://www.sss.gov/Registration/Why-RegisterIt is the LawVirtually all male U.S. citizens, regardless of where they live, and male immigrants, whether documented or undocumented, residing in the United States, who are 18 through 25, are required to register with Selective Service.
The law says men must register with Selective Service within 30 days of their 18th birthday. That means men are required to register with Selective Service sometime during the 30 days before their 18th birthday, their 18th birthday, and the following 29 days after their 18th birthday – that is a 60-day registration period.Men who do not register with Selective Service within the 60-day window are technically in violation of the law and should register as soon as possible. Late registrations are accepted up to the 26th birthday. However, once a man reaches his 26th birthday and still has not registered with Selective Service, it is too late!