When you transport passengers across state lines:
Correct. Federal interstate minimum age is 21. Drivers under 21 may operate intrastate (within their state) only.
CDL Practice Question #440
Category: Passenger
Why this question matters
This question is one of 58 in our Passenger bank. The reasoning above comes directly from the AAMVA CDL Manual, the source document used by every U.S. state DMV. Memorizing the underlying rule — not just the letter answer — is what separates passing on the first attempt from a return trip and another fee.