Young men must register within 30 days of their 18th birthday. Go to any post office and ask for a Selective Service Registration card. Fill in the card and hand the card with some identification (such as your driver’s license) to the postal clerk. Remember, failure to register is a serious offense, and you could be prosecuted, face a fine, or be put in jail. Registration is also a requirement for federal student aid, job training benefits, and federal employment.