32 C.F.R. § 1624.3 : National Defense — OTHER REGULATIONS RELATING TO NATIONAL DEFENSE — SELECTIVE SERVICE SYSTEM — INDUCTIONS — Age selection groups

Age selection groups are established as follows:

(a) The age 20 selection group for each calendar year consists of registrants who have attained or will attain the age of 20 in that year.
(b) The age 21 selection group for each calendar year consists of registrants who have attained or will attain the age of 21 in that year and, in like manner, each age selection group will be so designated through age group 25.
(c) The age 26 through 34 selection groups consist of registrants who meet the following three criteria:
(1) They have attained or will attain the age of 26 through 34, respectively, during the calendar year; and
(2) They have been previously ordered to report for induction but have not been inducted; and
(3) They have been classified in one of the following classes:
(i) Class 1-D-D.
(ii) Class 2-D.
(iii) Class 3-A.
(iv) Class 4-B.
(v) Class 4-F.
(d) The age 19 selection group for each calendar year consists of registrants who have attained the age of 19 in that year.
(e) The age 18 selection group shall consist of registrants who have attained the age of 18 years and six months and who have not attained the age of 19 years in the order of their dates of birth with the oldest being selected first.

32 C.F.R. § 1624.3