20 C.F.R. § 416.801
An applicant for benefits under title XVI of the Act shall file supporting evidence showing the date of his birth if his age is a condition of eligibility for benefits or is otherwise relevant to the payment of benefits pursuant to such title XVI. Such evidence may also be required by the Administration as to the age of any other individual when such other individual's age is relevant to the determination of the applicant's eligibility or benefit amount. In the absence of evidence to the contrary, if the applicant alleges that he is at least 68 years of age and submits any documentary evidence at least 3 years old which supports his allegation, no further evidence of his age is required. In the absence of evidence to the contrary, if a State required reasonably acceptable evidence of age and provides a statement as to an applicant's age, no further evidence of his age is required unless a statistically valid quality control sample has shown that a State's determination of age procedures do not yield an acceptable low rate of error.
20 C.F.R. §416.801