14 CFR §121.383

1. (a)No certificate holder may use any person as an airman nor may any person serve as an airman unless that person—
   1. (1)Holds an appropriate current airman certificate issued by the FAA;
   2. (2)Has in his or her possession while engaged in operations under this part—
      1. (i)Any required appropriate current airman and medical certificates; or
      2. (ii)A temporary document issued in accordance with paragraph (c) of this section; and
   3. (3)Is otherwise qualified for the operation for which he is to be used.
2. (b)Each airman covered by paragraph (a)(2) of this section shall present his or her certificates or temporary document for inspection upon request of the Administrator.
3. (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.
4. (d)No certificate holder may use the services of any person as a pilot on an airplane engaged in operations under this part if that person has reached his or her 65th birthday.
5. (e)No pilot may serve as a pilot in operations under this part if that person has reached his or her 65th birthday.