I've been wondering if it's possible that guy is wearing weights like lee... if so he is yet to take them off and even if he goes 8 gates we still won't see his full potential
Naaah it wont matter 8th gates is certain death when you use it so it shouldnt matter if youre wearing weights or not your gonna pay the ultimate price which is death.
Even if he isn't wearing weights, Gai has been fighting for god knows how long. I'd guess the constant fighting since He and kakashi came to save Naruto from Obito has affected him quite abit.