20 CFR 219.20: When evidence of age is required.

(a) Evidence of age is required when an employee applies for an annuity under the Railroad Retirement Act or for Medicare coverage under title XVIII of the Social Security Act.

(b) Evidence of age is also required from a person who applies for a spouse's or divorced spouse's, widow's, widower's, surviving divorced spouse's, parent's, or child's annuity under the Railroad Retirement Act, or for Medicare coverage under title XVIII of the Social Security Act.