This is how you would do it using the latest version of angular, and building custom validation directives that use AngularJS's validation framework:

Step 1: Add Some Style

This is to make things look nice...

<!-- Optional theme -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap-theme.min.css">

<!-- Latest compiled and minified JavaScript -->
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>

<style>
  ul {
    margin: 0;
    padding:0;
  }
</style>

Step 2: Add AngularJS Libraries

You need the core AngularJS libraries and ngMessages:

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.4.6/angular.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.4.6/angular-messages.min.js"></script>

Step 3: Define your Validation Directives

Yes, I know there are already pre-defined AngularJS directives for "required" and "max length", but this is an SO answer and it's important that you know how to define ones yourself.

app.directive('rqrd', function() {
  return {
    restrict: 'A',
    require: 'ngModel',
    link: function(scope, element, attr, ngModel) {
      ngModel.$validators.rqrd = function(modelValue, viewValue) {
        var value = modelValue || viewValue;
        return value != null && value != undefined && value != '';
      }
    }
  }
});

app.directive('max', function() {
  return {
    restrict: 'A',
    require: 'ngModel',
    link: function(scope, element, attr, ngModel) {
      var maxValue = parseInt(attr.max);
      ngModel.$validators.max = function(modelValue, viewValue) {
        var value = modelValue || viewValue;
        return value.length > 0 && value.length <= maxValue;
      }
    }
  } 
});

app.directive('startsWith', function() {
  return {
    restrict: 'A',
    require: 'ngModel',
    link: function(scope, element, attr, ngModel) {
      ngModel.$validators.startsWith = function(modelValue, viewValue) {
        var value = modelValue || viewValue;
        return value && value.length > 0 && value.indexOf(attr.startsWith) == 0;
      }
    }
  } 
});

Step 4: Use your Validation Directives

<form name="form">

  Favorite Color   <br />
  <input name="color" ng-model="color" rqrd max="10"  />  
  <ul ng-messages="form.color.$error">
     <li ng-message="rqrd" class="label label-danger">This is required</li>
     <li ng-message="max" class="label label-danger">Max 10 chars</li>
  </ul> 
  Name <br />
  <input name="name" ng-model="name" starts-with="Z"  /> 
    <ul ng-messages="form.name.$error">
     <li ng-message="rqrd" class="label label-danger">Please enter an Age</li>
     <li ng-message="startsWith" class="label label-danger">Must start with Z</li>
  </ul> 

</form>

Checking that Form is Valid

if ($scope.form.$valid) {
   ...
}

    var app = angular.module('app', ['ngMessages']);

    app.controller('ctrl', function($scope) {
       
    });

    app.directive('rqrd', function() {
      return {
        restrict: 'A',
        require: 'ngModel',
        link: function(scope, element, attr, ngModel) {
          ngModel.$validators.rqrd = function(modelValue, viewValue) {
            var value = modelValue || viewValue;
            return value != null && value != undefined && value != '';
          }
        }
      }
    });

    app.directive('max', function() {
      return {
        restrict: 'A',
        require: 'ngModel',
        link: function(scope, element, attr, ngModel) {
          var maxValue = parseInt(attr.max);
          ngModel.$validators.max = function(modelValue, viewValue) {
            var value = modelValue || viewValue;
            return value.length > 0 && value.length <= maxValue;
          }
        }
      } 
    });

    app.directive('startsWith', function() {
      return {
        restrict: 'A',
        require: 'ngModel',
        link: function(scope, element, attr, ngModel) {
          ngModel.$validators.startsWith = function(modelValue, viewValue) {
            var value = modelValue || viewValue;
            return value && value.length > 0 && value.indexOf(attr.startsWith) == 0;
          }
        }
      } 
    });

    <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.4.6/angular.min.js"></script>
    <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.4.6/angular-messages.min.js"></script>
    <!-- Latest compiled and minified CSS -->
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css">

    <!-- Optional theme -->
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap-theme.min.css">

    <!-- Latest compiled and minified JavaScript -->
    <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>

    <style>
      ul {
        margin: 0;
        padding:0;
      }
    </style>

    <h3>Example heading </h3>
    <div ng-app="app" ng-controller="ctrl">
    <form name="form">

      Favorite Color   <br />
      <input name="color" ng-model="color" rqrd max="10"  />  
      <ul ng-messages="form.color.$error">
         <li ng-message="rqrd" class="label label-danger">This is required</li>
         <li ng-message="max" class="label label-danger">Max 10 chars</li>
      </ul> 
      Name <br />
      <input name="name" ng-model="name" starts-with="Z"  /> 
        <ul ng-messages="form.name.$error">
         <li ng-message="rqrd" class="label label-danger">Please enter an Age</li>
         <li ng-message="startsWith" class="label label-danger">Must start with Z</li>
      </ul> 
    </form>
      
    </div>

Angular already has a validation framework built in, which includes capabilities to add custom validations. This is done by creating custom directives which define validation functions, then adding those directives as attributes to your input. IE from the Angular example, we create this custom integer directive:

app.directive('integer', function() {
  return {
    require: 'ngModel',
    link: function(scope, elm, attrs, ctrl) {
      ctrl.$validators.integer = function(modelValue, viewValue) {
        if (ctrl.$isEmpty(modelValue)) {
          // consider empty models to be valid
          return true;
        }

        if (INTEGER_REGEXP.test(viewValue)) {
          // it is valid
          return true;
        }

        // it is invalid
        return false;
      };
    }
  };
});

Then add it to our input:

<input type="number" ng-model="size" name="size"
           min="0" max="10" integer />{{size}}<br />

And we can then access its validation status by querying form.size.$error.integer

A very nice framework in github https://github.com/turinggroup/angular-validator

<div class="col-sm-10">


<input  type = "text"
 name = "blur"
 validate-on="blur"
  class = "form-control"
ng-model = "form.blur"
  ng-pattern="/regex/"
  invalid-message="'You must enter the word `regex`'"
  required-message="'Yo! This field is required..'"
  required></div>

Demo here

Another well detailed example here