what age to cross state lines with a chauffeur license?

Depends , what kind of vehicle?

 

The age problem is more for those with the hazmat endorsement. Yet some states may not consider you an adult until your 21. Lame I know, I remember those days.

 

To drive a class 8 across state lines you need to be 21

 

A chauffeur license is not a class 8 license.

I'm not sure but I believe that if you are doing any sort of commercial commerce you must be 21 years old. Check with one of the RV hauling companies, they would know for sure as many of their haulers use a chauffeur license if available from the state they are from.