I dont know how NATS works but in some other countries this is the standard procedure.
If you 17, first apply for ATC. If you lucky enough to get accepted straight away then fantastic as you can work as an air traffic assistant (ATSA), learn the ropes then get sent on a control course to become ATC when you ready.
If not, then go study something else that you have an interest in, then at least you will always have something to fall back on! Then apply.
I know that ATNS (SA) prefers you to have a degree before you apply although not a necessity (IT or BSc Preferred).
I did my 3 year IT Degree first (which is really boring but at least I have it), then only did I apply. Remember that an ATC rating you can lose if you dont work for a certain period of time (2 years I think it is), no one can take a degree or diploma away from you...