14 CFR § 121.383 - Airman: Limitations on use of services.
(1) Holds an appropriate current airman certificate issued by the FAA;
(2) Has in his or her possession while engaged in operations under this part -
(i) Any required appropriate current airman and medical certificates; or
(ii) A temporary document issued in accordance with paragraph (c) of this section; and
(3) Is otherwise qualified for the operation for which he is to be used.
(c) A certificate holder may obtain approval to provide a temporary document verifying a flightcrew member's airman certificate and medical certificate privileges under an approved certificate verification plan set forth in the certificate holder's operations specifications. A document provided by the certificate holder may be carried as an airman certificate or medical certificate on flights within the United States for up to 72 hours.
(e) No pilot may serve as a pilot in operations under this part if that person has reached his or her 65th birthday.