Fifty-seven percent. That’s the amount of his lifetime Rıdvan Yılmaz has spent at Beşiktaş.   The 19-year-old left back joined the club in 2009, at the age of eight. He was born in the working class Gaziosmanpaşa district of Istanbul and grew up in nearby Sultangazi. Like so many kids in the area, Rıdvan honed…