I am a 15 year old ham, and just got my Extra class. I was really bummed when I figured out I needed to be 18 to be a Volunteer Examiner administer. Why do they make that rule?
Congress sets the rules the FCC has to follow, and the rule in particular requiring an age limit is Title 47, Volume 5, Part 97, Subpart F:
§ 97.509 Administering VE requirements.
(b) Each administering VE must:
(2) Be at least 18 years of age;
It would take an act of Congress to change this rule. I haven't discovered the reason for this rule, but if you look through the amendments to Part 97 over time you may be able to discover which congress made the change, and reading the congressional record may indicate why.
The licence is a legal document.. A binding contract. A person has to be 18 to sign a binding legal contract. Very valid reasons.