I'm assuming the OP is here on a visa. Her parents may or may not be US citizens. This happens a lot in Florida. Parents move from the UK. Some stay here on work visas. Some go for their citizenship. Their children are allowed to stay here under their parents visas until they are 18. At that time, they must apply for a new visa to remain here or return to the UK. I have a neighbor going through this right now.
As for the UK provisional license being used for ID, that is tricky. My daughter recently went to a bar with a girl who is working at Epcot under the international college program. The bar would not accept her UK license as id to prove she was 21. In fact, the girl is 23, but the server at the bar was not familiar with the UK id and would not accept it.