Eligibility for some types of benefits under the Social Security Act will require proof of a claimant's age. For example, in order to be eligible for retirement benefits, a claimant must demonstrate that he or she has reached retirement age. Age is also a factor for entitlement to spousal benefits, child's benefits, widow's and widower's benefits, and parent's benefits. The best evidence of age, in order to establish eligibility to the Social Security Administration (SSA), is a birth certificate. Any credible evidence of age that a claimant submits will be accepted and considered by the SSA.