20 CFR § 404.716 - Type of evidence of age to be given.
(a) Preferred evidence. The best evidence of your age, if you can obtain it, is either: a birth certificate or hospital birth record recorded before age 5; or a religious record which shows your date of birth and was recorded before age 5.
(b) Other evidence of age. If you cannot obtain the preferred evidence of your age, you will be asked for other convincing evidence that shows your date of birth or age at a certain time such as: an original family bible or family record; school records; census records; a statement signed by the physician or midwife who was present at your birth; insurance policies; a marriage record; a passport; an employment record; a delayed birth certificate, your child's birth certificate; or an immigration or naturalization record.