미성년자 체크

//미성년자 체크
  var jumin = f.userNo1_1.value+f.userNo1_2.value;
  var today = new Date();

  var now_year=today.getFullYear();
  var now_month=today.getMonth()+1;
  var now_day=today.getDate();

  var birth_year=jumin.substring(0,2);
  var birth_month=jumin.substring(2,4);
  var birth_day=jumin.substring(4,6);

  var sex=jumin.substring(6,7);
  
  if(sex=="1" || sex=="2"){
   var full_year="19"+birth_year;
  }else if(sex=="3"||sex=="4"){
   var full_year="20"+birth_year;
  }
  var age=now_year-full_year;

  var man_age=age;

  if(now_month<birth_month){
   man_age=age-1;
  }else if(now_month==birth_month){
    if(now_day<birth_day){
     man_age=age-1;
    }
  }

  if(man_age>20){  
   //alert("성인");
  }else{
   alert( "만 20세 이상만 가입 가능합니다.");
   return;
  }