Spirit Rental Car

Do you have a full driving license for at least one year? And what is your age?

Then look here:-

At STEP2, click on the link "IMPORTANT INFORMATION' displayed to the right of the car photo of your choice. This will open another smaller window and if you click on "DRIVER" you will see what age restrictions there may be and any associated fees. Try a few different car models / suppliers, as they do differ.

OK, I did look as well. I see FOX accept 19 year old, they say this:

AGE Minimum age for renters and drivers is 19. Minimum age for renters and drivers on government orders is 18. Renters and drivers under the age of 25 are subject to a surcharge - UNDER AGE 25 SURCHARGE is USD/20.00 to USD/26.00 per day (depending on the rental location). UNDER AGE 21 YOUNG RENTER SURCHARGE is USD/25.00 to USD/35.00 per day (depending on the rental location). This Age Policy applies at all FOX Corporate locations.

They are the only supplier who accepts 19 years old driver against NO fee.