I'm 6ft 1(and a quarter) inches and have relatively short legs compared to body length. In the Tincan, and now Hawk, my seat still has to be right down and the rudder pedals all the way back. This is getting into the realms of forming a gap between my thigh and seat which would not be good for my femur should I use the exploding furniture. There are few of my mates who are considerably bigger but many have big variations in limb length.
In my UAS days, many girls were not accepted for lack of functional reach and a good mate who was sponsored and nearly finished EFT could not go FJ because of excessive thigh length. Now flys spinning whirly death machines.
Back to the question, let the lad apply and if he is too big then you cant help it. There are plenty more hurdles and hoops!
Good luck
Ray