Anyone who drives a commercial vehicle is required to obtain a commercial drivers’ license (or CDL). In order to qualify for the CDL, the driver must satisfy certain requirements with respect to his or her hearing and vision (for example, the driver cannot be color blind), and must also be at least 21 years old. To maintain the license, the driver must undergo a physical exam at least every two years, and must also not have any type of mental issues that might prevent safe driving.