Former British number one Andrew Castle has declared that Roger Federer has been able to stay at the top of men's tennis thanks to his competitive spirit and enduring love for the sport.
Federer won at Wimbledon last year aged 30 and the 17-time Grand Slam champion continues to be ranked among the top three players in the world.
Castle thinks that Federer has been spurred on to stay at the top level by his rivalries with Andy Murray, Rafael Nadal and Novak Djokovic.
He told BBC Sport: "Thirty-one years of age is quite old to be a world class tennis player.
"He clearly works extremely hard and never gets injured. It's the freshness. He just loves the game.
"He may be a third of a step slower than he was five, six, seven years ago but he's flourished with the rivalry of Nadal, Djokovic and Murray and that rivalry has reinvigorated him. It's thrilling to see him competing against the younger guys."
Federer goes up against Murray in the Australian Open semi-finals this morning for the right to play Djokovic in Sunday's final.
