Age for car rental

In the states, you have to be 25 to rent a car - does anyone know if that same policy applies on the island? My nephew is coming down for a few days, and I'm sure he'd rather strike out on his own for a bit rather than being saddled with his old geezer of an uncle?

I did some quick looking and only found one agency that mentioned an age restriction. It was 18 but I would imagine it might vary between rental agencies. I would check directly with the agency of your choice for confirmation.