problem js

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
   "http://www.w3.org/TR/html4/strict.dtd">
<html lang="en">
<head>

<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<meta name="language" content="dutch">
<meta http-equiv="Content-Style-Type" content="text/css">
<meta name="description" content="x">

<title>x</title>

<link rel="stylesheet" type="text/css" href="verification.css">
<link rel="shortcut icon" type="image/x-icon" href="http://www.x.nl/favicon.ico">

	<script language="javascript" type="text/javascript">
		function checkAge()
		{
			/* the minumum age you want to allow in */
			var min_age = 16;

			var year = parseInt(document.forms["age_form"]["year"].value);
			var month = parseInt(document.forms["age_form"]["month"].value);
			var day = parseInt(document.forms["age_form"]["day"].value);

			var theirDate = new Date((year + min_age), month, day);
			var today = new Date;

			if (month == 0){
			  alert("month?");
			  return false;
			}
			if (day == 0){
			  alert("What day were you born?");
			  return false;
			}
			if ( (today.getTime() - theirDate.getTime()) < 0) {
				alert("Youre too young");
				return false;
			}
			else {
				return true;
			}
		}
	</script>


</head>
<body>

<div id="container">

<div align="center">
<form action="http://www.x.nl/home" method="post" name="age_form">
<select id="dag" name="day">
 	<option>00</option>
 	<option>01</option>
	<option>02</option>
	<option>03</option>
	<option>04</option>
	<option>05</option>
	<option>06</option>
	<option>07</option>
	<option>08</option>
	<option>09</option>
	<option>10</option>
	<option>11</option>
	<option>12</option>
	<option>13</option>
	<option>14</option>
	<option>15</option>
	<option>16</option>
	<option>17</option>
	<option>18</option>
	<option>19</option>
	<option>20</option>
	<option>21</option>
	<option>22</option>
	<option>23</option>
	<option>24</option>
	<option>25</option>
	<option>26</option>
	<option>27</option>
	<option>28</option>
	<option>29</option>
	<option>30</option>
	<option>31</option>
</select>

<select id="maand" name="month">
 	<option>00</option>
	<option>01</option>
	<option>02</option>
	<option>03</option>
	<option>04</option>
	<option>05</option>
	<option>06</option>
	<option>07</option>
	<option>08</option>
	<option>09</option>
	<option>10</option>
	<option>11</option>
	<option>12</option>
</select>

<select id="jaar" name="year">
 	<option>2013</option>
 	<option>2013</option>
	<option>2012</option>
	<option>2011</option>
	<option>2010</option>
	<option>2009</option>
	<option>2008</option>
	<option>2007</option>
	<option>2006</option>
	<option>2005</option>
	<option>2004</option>
	<option>2003</option>
	<option>2002</option>
	<option>2001</option>
	<option>2000</option>
	<option>1999</option>
	<option>1998</option>
	<option>1997</option>
	<option>1996</option>
	<option>1995</option>
	<option>1994</option>
	<option>1993</option>
	<option>1992</option>
	<option>1991</option>
	<option>1990</option>
	<option>1989</option>
	<option>1988</option>
	<option>1987</option>
	<option>1986</option>
	<option>1985</option>
	<option>1984</option>
	<option>1983</option>
	<option>1982</option>
	<option>1981</option>
	<option>1980</option>
	<option>1979</option>
	<option>1978</option>
	<option>1977</option>
	<option>1976</option>
	<option>1975</option>
	<option>1974</option>
	<option>1973</option>
	<option>1972</option>
	<option>1971</option>
	<option>1970</option>
	<option>1969</option>
	<option>1968</option>
	<option>1967</option>
	<option>1966</option>
	<option>1965</option>
	<option>1964</option>
	<option>1963</option>
	<option>1962</option>
	<option>1961</option>
	<option>1960</option>
	<option>1959</option>
	<option>1958</option>
	<option>1957</option>
	<option>1956</option>
	<option>1955</option>
	<option>1954</option>
	<option>1953</option>
	<option>1952</option>
	<option>1951</option>
	<option>1950</option>
</select>

<input type="submit" id="submit" name="_send_date_" value="Check" onClick="return checkAge()">
</form>
</div>

</div>
<script type="text/javascript">
	var _gaq = _gaq || [];
	_gaq.push(['_setAccount', 'UA-53192426-47']);
        _gaq.push(['_addDevId', 'i7k94']); //

	_gaq.push(['_trackPageview']);

	(function() {
		var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
		ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
		var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
	})();
</script>

</body>
</html>