context: Martina started bouncing tennis balls at two years old and at the age of four she played in her first tournament. In 1993, Hingis became the youngest ever Grand Slam junior series winner when he conquered Juniors singles crown at Roland Garros at the age of 12. The following year he successfully defended his championship and also won at Wimbledon. Hingis was already the junior unit in the world.
question: At what age did Martina Hingis start playing tennis?
answers.text: two years old