Many car rental companies require that you be at least 25 to rent a car.
In most places you also have to be at least 21 to be 22 years old.
Re: Car Rental- IIRC Sebastian Vettle, now multi-F1 World Championship Driver tried to rent a car in Monaco on Race Weekend and being denied to do so because He was too young 18+ and F1 Driving Championship didn’t get to help him anyway.
So He just bought a new car, drove it till he was done with it and sold it back to the Dealership when done with it...