FWIW...
I never registered...
“* Men born from March 29, 1957, through December 31, 1959, were not required to register because registration was suspended for several years in the late 1970s. “
http://www.sss.gov/Records2.htm
When I was 18 and 19 there was no way TO register.
Yes, there was a period of years where one did not have to register, as I recollect Obama is not within that period.