That's a good book for taking the test. If your planning on getting a Red Tail I highly recommend William Oaks book on falconry, I can't recall the name of the book but if you look up William Oaks you should be good.
18 is as good as time as any to start, I am only 16 and got my first bird when I was barley 13
Falconry is a great sport and once your in it you will love it!