For purposes of this subsection, the “reduction period” for an individual’s old-age, wife’s, husband’s, widow’s, or widower’s insurance benefit is the period—

(A) beginning— (i) in the case of an old-age insurance benefit, with the first day of the first month for which such individual is entitled to such benefit, (ii) in the case of a wife’s or husband’s insurance benefit, with the first day of the first month for which a certificate described in paragraph (5)(A)(i) is effective, or (iii) in the case of a widow’s or widower’s insurance benefit, with the first day of the first month for which such individual is entitled to such benefit or the first day of the month in which such individual attains age 60, whichever is the later, and

(B) ending with the last day of the month before the month in which such individual attains retirement age.