14 CFR § 65.71

To be eligible for a mechanic certificate and associated ratings, a person must—

Be at least 18 years of age;

Be able to read, write, speak, and understand the English language, or in the case of an applicant who does not meet this requirement and who is employed outside of the United States by a U.S. air carrier, have his certificate endorsed “Valid only outside the United States”;

Have passed all of the prescribed tests within a period of 24 months; and

Comply with the sections of this subpart that apply to the rating the applicant seeks.

A certificated mechanic who applies for an additional rating must meet the requirements of § 65.77 and, within a period of 24 calendar months, pass the tests prescribed by §§ 65.75 and 65.79 for the additional rating sought, except as provided in § 65.75(d).