Correct me if I am wrong, but do you not have to be 20+ to be a CI given that some cadets can carry on until that age?
I was a CI and am looking into it again. Don't worry if you don't know much about the ATC or the RAF as you will be shown everything.
Best thing to do is to ring your local squadron (You can find the number on the air cadets site) and they can advise you further. They usually invite you for a look around the squadron and a chat.
Just a thought, maybe you shouldn't be posting such comments about your old ATC? A lot of people associated with the RAF and ATC read this, and I'm guessing some may not appreciate the comment.
Anyway, good luck with it.