If you failed to register with Selective Service, Section 12(g) of the Military Selective Service Act allows non-registrants to receive benefits under specific conditions. As a veteran, or part-time National Guard or Reservist, you satisfy those conditions with your DD Form 214 showing the dates of your military service, or a current military ID card if still on active duty or a member of the National Guard and Reserves. These documents serve...
"If you failed to register with Selective Service, Section 12(g) of the Military Selective Service Act allows non-registrants to receive benefits under specific conditions. As a veteran, or part-time National Guard or Reservist, you satisfy those conditions with your DD Form 214 showing the dates of your military service, or a current military ID card if still on active duty or a member of the National Guard and Reserves. These documents serve as evidence that your failure to register was not knowing and willful."
Even though I was on active duty and a Sergeant they managed to make it sound like I was a draft dodging hippy malcontent or something. So I filled out the required documents sent copies of my enlistment and a notarized letter from my commander stating that I was in fact a Soldier in good standing.. The situation was resolved but it was embarrassing and caused my folks extra worry that was un-needed.
My advice is just do it and avoid any stupid shit down the road.
https://www.sss.gov
“…To furnish manpower to the Defense Department during a national emergency, to manage alternative service for men classified as conscientious objectors, and to register, with only a few exceptions, all male U.S. citizens and male immigrants residing in the United States who are ages 18 through 25...”