There’s some information in this thread: Lord lieutenant's cadet queries and you might find more if you use the forum search function.
Generally when nominations are due, WHQ will email all units with a request for nominations and the criteria.
Have you spoken to your Sqn about it?
You should be over 16 and able to remain in post for the 12 months, with the ability to attend events, nominees are usually SNCO (although off the top of my head I can’t recall if that is set - but a senior rep of good quality would by default imply senior NCO).
Edit: missed the CCF bit, I’m not sure if they run through the local ATC hierarchy or their TEST staff, so probably substitute WHQ for the relevant CoC and perhaps someone of the CCF breed here will be able to confirm.