How to validate age using Angularjs?

I don't have any code from you to base an answer off of, but here is a function to help you identify the correct age:

$scope.dateDiff = function(birthMonth, birthDay, birthYear) {
    var todayDate = new Date(),
        todayYear = todayDate.getFullYear(),
        todayMonth = todayDate.getMonth(),
        todayDay = todayDate.getDate(),
        age = todayYear - birthYear; 

    if (todayMonth < birthMonth - 1)
    {
      age--;
    }

    if (birthMonth - 1 === todayMonth && todayDay < birthDay)
    {
      age--;
    }
    return age;
};

$scope.dateDiff(8,15,1963); // return as 50 as birthday has passed
$scope.dateDiff(9,15,1963); // return as 49 as birthday has not yet happened

In your HTML you could use ng-options to allow the user to select dates from dropdown list.

Day <select ng-model="selectedDay" ng-options="day as day.date for day in days"></select>

Here is a full working example.

Being that you're new to Angular, make sure you take the time to learn how this code works. ng-options may seem a little confusing at first, but when you start to understand Angular Principles, it shouldn't be a problem.