Floyd Mayweather is 45. He could probably do this when he’s 75. The unbeaten Hall of Famer knocked out Mikuru Asakura in the second round of a scheduled three-round exhibition in the Super RIZIN headliner in Saitama, Japan. The 30-year-old Japanese mixed martial artist was game and had his moments, landing a few eye-catching punches. However, no MMA fighter has the boxing skills to compete on an even level with one of the greatest practitioners of the sweet science, even one who’s in his mid-40s. And that’s by design. Mayweather has said he doesn’t want to trade punches with anyone…