How old was Johnny when he first entered high school?

When 16-year-old Johnny first entered high school four years ago,he worked very hard and always got good grades. Besides doing well in his lessons, he was also very active in sports. He used to get up very early every morning to practise running. He never took the school bus to school. He always ran there. He even won a silver medal (奖章，纪念章) in the 200-meter race at the school’s sports meet a year ago. As a reward, his parents bought him something he had been wanting to have for a long time—a computer.
    Then things began to change. He stopped getting up early and never ran to school.  His interest in sports suddenly disappeared. Sometimes he got up so late that he would miss the school bus and thus miss school Soon his school work began to suffer.
    One day, in the middle of the night, his mother saw lights from Johnny’s room. She went in and discovered the cause of Johnny’s change. Johnny had been playing computer games late into the night ever since he had the computer. He had neglected his studies and suffered from lack of sleep. This must be stopped.
    The next day, she had a serious talk with Johnny. Instead of threatening to take away his computer, she told him he was old enough to learn to have some control over himself.  Johnny was happy he had such a wonderful mother and promised her to correct himself.