People decline at different rates. It depends what your crutch is. Mayweather's ability is founded on reflexes and speed. Those are the first to go. But there is no sign that either of these attributes are on the decline. He may be on the tail end of this prime but Mayweather is still in his prime. Extending or maximizing your prime I think a lot has to do with Mayweather always staying fit, active, and not having any real bad habits to his body even in retirement.