Who can drive a farm use vehicle?

If it's a registered farm vehicle which wouldn't be considered a Commercial Motor Vehicle without the farm exemption, any licenced driver can operate it.

In the case of vehicles which would normally require a CDL, the farmer, immediate family members of the farmer may operate it within a 150 mile radius of that farm, only for purposes directly supporting that farm, without requiring a CDL. However, anyone operating it more than 150 miles from the farm, and anyone who isn't either immediate family members of the farmer or direct employees (W-2 employees, not 1099 employees) must have a CDL.