Select Date, DDL Date, Custome Validation in Csharp .net

 <script type="text/javascript">
 function CustDateValidator_ServerValidate(sender, args) {
            var dateString = document.getElementById("ddlday").value + "/" + document.getElementById("ddlmonth").value + "/" + document.getElementById("ddlYear").value;
            var regex = /(((0[1-9])|([1-31]))\/([1-9])|(0[1-9])|(1[0-2]))\/((19|20)\d\d)$/;
               if (regex.test(dateString)) {
                var parts = dateString.split("/");
                var dt = new Date(parts[1] + "/" + parts[0] + "/" + parts[2]);
                args.IsValid = (dt.getDate() == parts[0] && dt.getMonth() + 1 == parts[1] && dt.getFullYear() == parts[2]);
            } else {
                args.IsValid = false;
            }
        }
 </script>
<%
protected void CustDateValidator_ServerValidate(object source, ServerValidateEventArgs args)
    {
        DateTime dt;
        //ddlYear
        DateTime dtc;
        args.IsValid = false;
        try
        {
            dtc = Convert.ToDateTime(ddlYear.SelectedValue + "/" + ddlmonth.SelectedValue + "/" + ddlday.SelectedValue);
            args.IsValid = true;
        }
        catch (Exception)
        {

            args.IsValid = false;
        }


    }
%>

 <asp:DropDownList ID="ddlYear" runat="server"  ClientIDMode="Static"  AutoPostBack="true" OnSelectedIndexChanged="ddlYearchange">
                                    <asp:ListItem Value="0" Selected="True">YYYY</asp:ListItem>
   </asp:DropDownList>
  <asp:DropDownList ID="ddlmonth" runat="server"  ClientIDMode="Static" AutoPostBack="true" OnSelectedIndexChanged="ddlmonthchange">
                                    <asp:ListItem Value="0" Selected="True">MM</asp:ListItem>
   </asp:DropDownList>
 <asp:DropDownList ID="ddlday" runat="server" ClientIDMode="Static" AutoPostBack="true" OnSelectedIndexChanged="ddldaychange">
                                    <asp:ListItem Value="0" Selected="True">DD</asp:ListItem>
   </asp:DropDownList>


  <asp:CustomValidator runat="server" ID="CustDateValidator" OnServerValidate="CustDateValidator_ServerValidate"
                                ClientValidationFunction="CustDateValidator_ServerValidate"  CssClass="errorMsg" ErrorMessage="Please select valid date"
                                ValidationGroup="Vg" />