title: Symfony2 custom minimum age validator - no error message displayed in twig?
body: <p>I have a minimum age custom validator which is straight forward enough:</p>
  
  <p><strong>The constraint(Minage.php)</strong></p>
  
  <pre><code>namespace MyCompany\VisitBundle\Component\Validator\Constraints;
  use Symfony\Component\Validator\Constraint;
  
  /**
   * @Annotation
   */
  class Minage extends Constraint
  {
      public $message = 'The user must be {{ age }} or over';
      public $age = 18;
  
      public function validatedBy()
      {
          return get_class($this).'Validator';
      }
  }
  </code></pre>
  
  <p><strong>The validator (MinageValidator.php)</strong></p>
  
  <pre><code>namespace MyCompany\VisitBundle\Component\Validator\Constraints;
  use Symfony\Component\Validator\Constraint;
  use Symfony\Component\Validator\ConstraintValidator;
  
  class MinageValidator extends ConstraintValidator
  {
      public function isValid($value, Constraint $constraint)
      {
          $minAge = strtotime(sprintf("-%s YEAR", $constraint-&gt;age));
          if(strtotime($value-&gt;format("Y-m-d")) &gt; $minAge)
          {
              $this-&gt;setMessage($constraint-&gt;message,
                                array('{{ age }}' =&gt; $constraint-&gt;age));
              return false;
          }
          return true;
      }
  }
  </code></pre>
  
  <p><strong>In my entity (stripping parts which aren't important)</strong></p>
  
  <pre><code>use MyCompany\VisitBundle\Component\Validator\Constraints as MyCompanyAssert;
  
  /**
   * @ORM\Column(name="birth_date", type="datetime")
   * @MyCompanyAssert\Minage(age="18")
   */
  private $birth_date;
  </code></pre>
  
  <p><strong>And in twig:</strong></p>
  
  <pre><code>{{ form_errors(form.birth_date) }}
  {{ form_widget(form.birth_date) }}
  </code></pre>
  
  <p>I know for sure the validator is returning false but my form refuses to show the error message All other validators (out-of-the-box not custom) work fine and show their respective errors. Any idea? </p>
  
  <p>Translations are disabled, so it won't be looking for a translation in a file.</p>
  
  <p>Thanks in advance.</p>
  
  <p><strong>UPDATE: <code>form_errors(form.birth_date)</code> does not work but <code>form_errors(form)</code> does? why is it assigned as a global form error?</strong></p>