Viist
http://www.sss.gov/ for more info.
What is the penalty for not registering?
If you do not register, you could be prosecuted and fined up to $250,000 and/or be put in jail for up to five years. Registration is also a requirement to qualify for Federal student aid, job training benefits, and most Federal employment.
(See also What Happens if I Don't Register?).
http://www.sss.gov/FSbenefits.htmCITIZENSHIP
The U.S. Immigration and Naturalization Service (INS) makes registration with Selective Service a condition for U.S. citizenship if the man first arrived in the U.S. before his 26th birthday.
http://www.sss.gov/FSmen.htmA non-registrant may not be denied any benefit if he can "show by a preponderance of evidence" that his failure to register was not knowing and willful. Offer as much evidence supporting your case, and as much detail, as possible.
Stating you didn't know you had to is not a preponderance of evidence. In the OP case, the person who did not register will most likely not be granted citizenship. If he did apply at age 29, he prob would be denied and then might be advised to re-apply after reaching the age of 31. Five years after he was last able to register for SS.