GS calculations have a random factor, so being "stuck" at 7 is no wonder at all.
Unless, randomness is now by far the no1 factor in GS calculations, the numbers and the data doesn't add up to make your claim valid, or at least doesn't excuse the lack of further examination.
Also 48 minutes is not ideal.
A clueless statement, borderline disturbing, given the assumption that you're the one who implemented development wise the influence of stamina to GS training...
About his training I'll just say one thing: he's 28.
I'll just say one thing: 4/18= 22,222%