Can a person temporarily operate a farm tractor on the high way without a driver license?

Yes. Farm machinery of all types can be driven on the road in order to move the equipment from one farm (or field) to another. The driver does not need a drivers license or even be of legal driving age but must follow the rules of the road just as any other driver. If the machinery is over width, special flaggers may be required. To my knowledge, joy riding is not permitted in any state (but I never hear of anyone getting fined if they do),