//根据日期计算年龄

<script language="javascript" type="text/javascript">
    function getAge(oldDate)
      {    
          oldDate = oldDate.replace("-","/");
         
          var   now=new Date(); 
          var   old=new Date(oldDate); //参数为出生年月,如1980/5/9  
          if(old >  now)
          {
             alert(" 当前日期不能小于生日 ");
             return; 
          }
          document.getElementById("age").value=now.getFullYear()-old.getFullYear();
          document.getElementById("age").readOnly = true;
      } 
     
    </script>

 <input id="age"/>
<input type="text"  id="dDate"  maxlength="19" onfocus="SetDate(this,'yyyy-MM-dd hh:mm:ss')" onpropertychange="getAge(this.value);"/>