http://xdsoft.net/jqplugins/datetimepicker/
Download Zip File From above mentioned Link ..

Now Copy .JS Files and .CSS File in Scripts Folder(If Not Exist , Then make a new folder and named it Scripts)

Now Follow the Code :
HTML HEAD(Section):
<head runat="server">
<title></title>
<link href="Scripts/jquery.datetimepicker.css" rel="stylesheet" type="text/css" />
</head>
AFTER Body Part :
<body>
<asp:TextBox ID = "TextBox1" runat = "Server"></asp:TextBox>
</body>
<script type="text/javascript" src="Scripts/jquery.js"></script>
<script type="text/javascript" src="Scripts/jquery.datetimepicker.js"></script>
<script type="text/javascript">
jQuery('[id$=TextBox1]').datetimepicker({
startDate: '+1971/05/01'//or 1986/12/08
});
</script>
</html>
OutPut :

This Might Help !!
:)