The minimum age to rent a car from Budget at Knoxville McGhee Tyson Airport is 20. Therefore, Budget car rentals at Knoxville McGhee Tyson Airport will charge an underage fee if you're under 25 and wish to rent a car. However, if you are aged above 18 and you intend to book a budget car for official military or state business, the Budget won't charge you an extra underage fee.