Prime or no prime, Xavi is almost 32 and is still fighting for best player awards every year, that's phenomenal and almost unheard of in a time where the sport is more physically demanding ever. I doubt even Messi or Iniesta will be this great and consistent when they're 32.
Xavi's fitness is remarkable. We thought that Cesc and Thiago had been brought to preserve Xavi, but on the contrary he has played more than any other midfielder so far with no signs of fatigue and actually seems fresher than all of them. His fitness is amazing.