This is the sixth time in her career to be ranked number one .
February 18 , 2013 - At age 31 , becomes the oldest female tennis player to be ranked number 1since computer rankings began in 1975 .
This is the sixth time in tennis player 's career to be ranked number one .
February 18 , 2013 - At age 31 , becomes the oldest female tennis player to be ranked number 1since computer rankings began in 1975 .