Any certificate filed pursuant to paragraph (1)(C)(ii)(III) shall be effective for purposes of this subsection—

(A) for the month in which it is filed and for any month thereafter, and

(B) for months, in the period designated by the individual filing such certificate, of one or more consecutive months (not exceeding 12) immediately preceding the month in which such certificate is filed;

except that such certificate shall not be effective for any month before the month in which he attains age 62.