The selection of persons for training and service under
section 3803 of this title shall be made in an impartial manner, under such rules and regulations as the President may prescribe, from the persons who are liable for such training and service and who at the time of selection are registered and classified, but not deferred or exempted:
Provided, That in the selection of persons for training and service under this chapter, and in the interpretation and execution of the provisions of this chapter, there shall be no discrimination against any person on account of race or color:
Provided further, That in the classification of registrants within the jurisdiction of any local board, the registrants of any particular registration may be classified, in the manner prescribed by and in accordance with rules and regulations prescribed by the President, before, together with, or after the registrants of any prior registration or registrations; and in the selection for induction of persons within the jurisdiction of any local board and within any particular classification, persons who were registered at any particular registration may be selected, in the manner prescribed by and in accordance with rules and regulations prescribed by the President, before, together with, or after persons who were registered at any prior registration or registrations:
And provided further, That nothing herein shall be construed to prohibit the selection or induction of persons by age group or groups under rules and regulations prescribed by the President:
And provided further, That—