ROTTERDAM - Roger Federer will target a return to the top of the rankings as the Rotterdam World Tennis tournament starts on Monday, with the Swiss aiming to become the oldest number one player in ATP history. The test begins at the Ahoy stadium when the 36-year-old, who claimed his 20th Grand Slam title a fortnight ago in Melbourne, returns to the Dutch port city for the first time since 2013. Top seed Federer starts in the first round against a qualifier in an event he has won twice before, lifting the trophy in 2005 and 2012.