<script type="text/javascript">
<!--

function getAge(){

  /* 今日の日付 */
  date = new Date();
  yy = date.getYear();
  mm = date.getMonth()+1;
  dd = date.getDate();

  if(yy<2000) yy += 1900;
  if(mm<10)   mm = "0"+mm;
  if(dd<10)   dd = "0"+dd;
  now = yy*10000 + mm*100 + dd;

  /* 誕生日 */
  doc = document.birth;
  var err = false;
  var Bmm = 0;
  var Bdd = 0;

  if(doc.Byear.value.length<1)  err = true;
  if(doc.Bmonth.value.length<1) err = true;
  if(doc.Bday.value.length<1)   err = true;

  if(err){
    window.alert("(´・∀・｀)ちゃんと入力しろぼけ。");

  }else{
    Bmm = doc.Bmonth.value;
    if(Bmm.length<2) Bmm = "0"+Bmm;

    Bdd = doc.Bday.value;
    if(Bdd.length<2) Bdd = "0"+Bdd;

    window.alert("あなたは"+Math.floor((now-(doc.Byear.value + Bmm + Bdd))/10000)+"歳ですか？");
  }
}

//-->
</script>


<div style="padding: 0.5em 0;">
<form method="POST" name="birth">
  <input type="text" name="Byear"  value="" onfocus="this.select()" size="6" maxlength="4">
  <input type="text" name="Bmonth" value="" onfocus="this.select()" size="4" maxlength="2">
  <input type="text" name="Bday"   value="" onfocus="this.select()" size="4" maxlength="2">
  <input type="button" value="おいくつ？" onclick="getAge()">
</form>
</div>