A_A is quite right, if you have good A-levels now.
oh, and I heard a rumour that if you excel in training you can be picked out as officer material. Is this true?
You may indeed be picked out but you will remain in the NCA stream as that is what you would have been recruited for. Having qualified as NCA you then have to excel once again to stand out as a brand new, no-nothing NCO with your elders who are already expert.
I would guess it is probably easier for an airman to make the jump than for NCA. The jump, SAC-Commission is potentially easier to demonstrate than NCO-Commision because the later will be in a group of excellence already.