You could possibly be charged with driving a vehicle without the owners consent, but more importantly if you are not a valid driver then you are driving without insurance.
Driving without insurance is illegal in Florida.
You should also be aware that the insurance you don't have doesn't just protect you against damaging the car. In the US, if you seriously injure someone in an accident they can and will come after you for their medical bills, which can run to hundreds of thousands of dollars. This is what your insurance covers you against (amongst other things). Unless you can afford to pay hundreds of thousands of dollars, don't drive without insurance.