5 C.F.R. § 338.601

A maximum-age requirement may not be applied in either competitive or noncompetitive examinations for positions in the competitive service except as provided by:

(a) Section 3307 of title 5, United States Code; or

(b) Public Law 93-259 which authorizes OPM to establish a maximum-age requirement after determining that age is an occupational qualification necessary to the performance of the duties of the position.