in the case of an individual who enrolls pursuant to paragraph (1) of this subsection, entitlement to benefits shall begin on—
(A)#
the first day of the second month after the month in which he enrolls,
(B)#
July 1, 1973 , or
(C)#
the first day of the first month in which he meets the requirements of subsection (a),
whichever is the latest;