TextBox控件只允许输入出生日期，并验证年龄不得小于18岁

<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>