Don't worry, the longer you wait the better chance you have of passing first time. Remember if you get your provisional you can have a years worth of practice before you take your test. I think this is another part of the governments idea to bring everything up to the age of 18. I too my test when I was 21, instead of having an old banger as my first car I am driving a Ford Focus 1.6 ghia, granted the insurance is a bit high but its so much nicer to drive than anything my mates have.