An individual may enroll in the insurance program established by this part only in such manner and form as may be prescribed by regulations, and only during an enrollment period prescribed in or under this section.

In the case of individuals who first satisfy paragraph (1) or (2) of section 1395o(a) of this title before March 1, 1966, the initial general enrollment period shall begin on the first day of the second month which begins after July 30, 1965, and shall end on May 31, 1966. For purposes of this subsection and subsection (d), an individual who has attained age 65 and who satisfies paragraph (1) of section 1395o(a) of this title but not paragraph (2) of such section shall be treated as satisfying such paragraph (1) on the first day on which he is (or on filing application would have been) entitled to hospital insurance benefits under part A.

In the case of an individual who first satisfies paragraph (1) or (2) of section 1395o(a) of this title on or after March 1, 1966, his initial enrollment period shall begin on the first day of the third month before the month in which he first satisfies such paragraphs and shall end seven months later. Where the Secretary finds that an individual who has attained age 65 failed to enroll under this part during his initial enrollment period (based on a determination by the Secretary of the month in which such individual attained age 65), because such individual (relying on documentary evidence) was mistaken as to his correct date of birth, the Secretary shall establish for such individual an initial enrollment period based on his attaining age 65 at the time shown in such documentary evidence (with a coverage period determined under section 1395q of this title as though he had attained such age at that time).