TextBox控件只允许输入出生日期，并验证年龄不得小于18岁

<form id="form1" runat="server">
    <div>
      <asp:Label ID="lblDob" runat="server" Text="Date of Birth :"></asp:Label>
      <asp:TextBox ID="txtDob" runat="server" onblur="Validate();"></asp:TextBox><asp:Label ID="Label3" runat="server" Text="(mm/dd/yyyy)"></asp:Label>
        <asp:RegularExpressionValidator ID="dateValRegex" runat="server" ControlToValidate="txtDob"
            ErrorMessage="*Please Enter a valid date in the format (mm/dd/yyyy)" ValidationExpression="^(0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])[- /.](19|20)\d\d$"
            ForeColor="Red"></asp:RegularExpressionValidator>
    </div>
    </form>

 <script>
        function Validate() {
                var enteredValue = document.getElementById(‘<%=txtDob.ClientID %>‘);
                var enteredAge = getAge(enteredValue.value);
                if (enteredAge < 18) {
                    alert("you are too young");
                    enteredValue.focus();
                    return false;
                }
            }
            function getAge(DOB) {
                var today = new Date();
                var birthDate = new Date(DOB);
                var age = today.getFullYear() - birthDate.getFullYear();
                var m = today.getMonth() - birthDate.getMonth();
                if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
                    age--;
                }
                return age;
            }

        </script>