PHP计算年龄

function age($YTD){
    $YTD = strtotime($YTD);
    $year = date('Y', $YTD);
    if(($month = (date('m') - date('m', $YTD))) < 0){
        $year++;
    }else if ($month == 0 && date('d') - date('d', $YTD) < 0){
        $year++;
    }
    return date('Y') - $year;
}