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To be quite honest, once solo, Air Cadet gliding could not really offer anything anyway. If you can get your young Air Cadet son to one of the RAFGSA clubs then I am sure they would be delighted to take him to the next level of gliding -
RAF Gliding & Soaring Association - Homepage. When the Air Cadet competition fleet was binned a few years ago* the only way to fly 'hot ships' in competition was via the RAFGSA. Also, if he were to join the RAF at any rank then the RAFGSA can take him forward to the very heights of national/international gliding competition if he has the dedication and aptitude - regardless of branch or trade.
I wish the best of luck to him...
LJ
*= Kestrel TX1 and Valiant TX1 were Janus C and ASW19 competition gliders.