In Spain, I've once been rejected to be registered as an extra driver because I had had my driving license for 11 months, and the car rental agency required that one should have a license for at least 1 year.
I know that in N-America, there is often an age below which one must either pay (a lot) more insurance, or below which one can not rent a car at all, nor be registered as an additional driver. If someone is above this age limit, but has had their license for a short time (i.e. less than a year), would this typically incur extra costs or cause problems when renting a car or when registering as an additional driver?
This may be relevant in case of liability insurance.