20 CFR § 404.331 - Who is entitled to wife's or husband's benefits as a divorced spouse.
You are entitled to wife's or husband's benefits as the divorced wife or divorced husband of an insured person who is entitled to old-age or disability benefits if you meet the requirements of paragraphs (a) through (e). You are entitled to these benefits even though the insured person is not yet entitled to benefits, if the insured person is at least age 62 and if you meet the requirements of paragraphs (a) through (f). The requirements are that -
(a) You are the insured's divorced wife or divorced husband and -
(1) You were validly married to the insured under State law as described in § 404.345 or you were deemed to be validly married as described in § 404.346; and
(2) You were married to the insured for at least 10 years immediately before your divorce became final;
(c) You are not married. (For purposes of meeting this requirement, you will be considered not to be married throughout the month in which the divorce occurred);
(d) You are age 62 or older throughout a month in which all other conditions of entitlement are met; and
(e) You are not entitled to an old-age or disability benefit based upon a primary insurance amount that is equal to or larger than the full wife's or husband's benefit.
(f) You have been divorced from the insured person for at least 2 years.