and it does seem a little young to be talking to the people who will be talking about the job (i havent even had a proper job- just helping this guy plaster and my dad with computers) so i could do with getting some good career knowledge behind me, and actually have some grades to show
Not at all - you are never too young - I was on "the books" of the careers Flt Lt who visited our school from the AFCO from the age of 13. He then saw me again each year to discuss my progress, and guided me through to selection for the 6th Form Scholarship when I was 17 (in which I was, happily, successful). By that time they'd had a chance to speak to me several times, and point me in the right direction as to what OASC would look for. Provided you are genuinely interested the sooner you get the AFCO involved the better IMO.
Personally I never involved the ATC in any of my direct "career" advice (sure, the training I had helped, and I always kept them up to date with how it was going) - mainly due to the fact they are volunteer Air Training Corps officers/staff - they are not trained in recruitment and selection, so won't necessarily be able to give you the best, or even correct, advice.