OPINION By Barry McGuigan Like Roger Federer in tennis, Gennady Golovkin is about to discover the cruel limitations imposed by Father Time. At his peak GGG was an amazing fighter, one of the best middleweights of all time, up there with Marvin Hagler, Roy Jones, James Toney, Mike McCallum, Ray Robinson and Carlos Monzon. Though coming off a stoppage win against Ryota Murata, that is of nil significance when going up a division to face Saul Canelo Alvarez in a trinity fight at 40 years old. Canelo is a much better fighter now than he was when the pair first met at middleweight in the same Las Vegas arena five years ago.