For those looking to Rent a Car in Cuba the rule is as following concerning the minimum age of the driver.
Renting a car upon arrival in Cuba
Although this can be a very complicated affair, some people like to live dangerously or leave their travel plans to the last moment. If you are one of these people then, the minimum age a rental car desk in Cuba will allow is 21 years old. If you are younger than 21 you will not be allowed to rent a car in Cuba.
Pre-booking a Rent a Car in Cuba
If you pre-book your rent a car in cuba AND you have the compulsory collection voucher then, the minimum age is 18 years old. The disparity in age minimums is directly related to the fact that car rental agencies feel more comfortable with pre-bookings and generally considers these to be made by more responsible (younger) people.
How about the validity of my driving license?