My advice would be if you go to University it may be useful to get a degree in something other than "Aviation Studies" . If you choose a degree like Maths, Geography, Chemistry or especially Computing I think it will give you another string to your bow. It will help if you get a partime job,bar work etc because it will give you something to talk about.
You are obviously interested in aviation so you can easily remain up to date in your spare time.
Having been an ATCO for over thirty years as long as you are a misfit
there does not seem to be standard ATCO type. I have seen people with top degrees not make it, and ruffians off the street who have been naturals.
Despite all of the selection tests I think it boils down to you either get it or you don't.
NATS are recruiting like crazy at the moment so why not apply now and if you fail you can reapply in two years, which you can use to go to Uni!
Also remember if you apply for NATS you may not get the discipline or posting you want.
Rgds
AyrTC