To be eligible for a flight navigator certificate, a person must-
(a) Be at least 21 years of age;(b) Be able to read, write, speak, and understand the English language;(c) Hold at least a second-class medical certificate issued under part 67 of this chapter within the 12 months before the date he applies; and(d) Comply with §§ 63.53 , 63.55 , and 63.57 .