age calculator

function birthday ($birthday)
  {
    list($year,$month,$day) = explode("-",$birthday);
    $year_diff  = date("Y") - $year;
    $month_diff = date("m") - $month;
    $day_diff   = date("d") - $day;
    if ($month_diff < 0) $year_diff--;
    elseif (($month_diff==0) && ($day_diff < 0)) $year_diff--;
    return $year_diff;
  }

echo birthday("1989-07-10");