How old do you have to be to rent a car in Panama City?

According to the Sixt website:
To rent a car in Panama with Sixt the driver must be 21 years of age or older and have had a driver's license for at least one year. For certain larger-sized vehicles, the minimum age may be 25 years or older. Those under 25 incur a a young driver surcharge of $5.00 per day with our car rental in Panama.