PHP 만나이 계산하기

function getManNai($birth_year,$birth_month,$brith_day){
        $birth_year = (int)$birth_year;
        $birth_month = (int)$birth_month;
        $brith_day = (int)$brith_day;

        $now_year = date("Y");
        $now_month = date("m");
        $now_day = date("d");

        if($birth_month < $now_month){
           $age = $now_year - $birth_year;
        }else if($birth_month == $now_month){
         if($brith_day <= $now_day)
          $age = $now_year - $birth_year;
         else
          $age = $now_year - $birth_year -1;
        }else{
           $age = $now_year - $birth_year-1;
        }
        return $age;
}
        
getManNai(1990,01,05);