I think what he's saying is that Witter can make welter weight tomorrow. He's getting old and would probably do him some good. He may even become better because of it. He has also been at Welter before.

If Witter was to move up as WBC light welter weight champion with an almost perfect record he would be a definate challenger for Mayweathers WBC Welter weight crown.
So either they would have to fight by WBC ranking rules, or Mayweather would be forced to run and hide.