First the Filipino great Manny Pacquiao launched his boxing comeback at 46 years old, and then came the improbable re-emergence from retirement this week, at the same age, of Englishman Ricky Hatton. Also returning to the professional ring – from the amateur ranks – after eight years’ absence is Hong Kong’s comparatively youthful Rex Tso Sing-yu, who, days before turning 38, has announced a bantamweight bout in Manila next month. Tso switched to amateur boxing in 2019 to target the Olympics. He...