When you go to your training class they'll take a photocopy of your license, which must be a chauffeur's license. It may very from state to state, but you must be 21 to get your chauffeurs here in MI.
At my center we basically couldn't proceed with the application process until we had a chauffeurs license. I'm assuming because you must be road tested as well as have on-road training during the class, and legally to operate a vehicle such as a package car, you must have the Chauffeur endorsement.
If in doubt, ask your HR rep, and you should be able to get a definitive answer, as opposed to speculation and personal experiences.