Why doesn't valid work when there are more than 10 characters in input?

Question

Zend Framework

Why doesn't valid work when there are more than 10 characters in input?

<?php
/**
 * @link      http://github.com/zendframework/ZendSkeletonApplication for the canonical source repository
 * @copyright Copyright (c) 2005-2016 Zend Technologies USA Inc. (http://www.zend.com)
 * @license   http://framework.zend.com/license/new-bsd New BSD License
 */

namespace Form\Controller;

use Form\Form\FormApplication;
use Zend\Form\Element\Button;
use Zend\Form\Element\Checkbox;
use Zend\Form\Element\Date;
use Zend\Form\Element\File;
use Zend\Form\Element\Hidden;
use Zend\Form\Element\Number;
use Zend\Form\Element\Select;
use Zend\Form\Element\Submit;
use Zend\Form\Element\Text;
use Zend\Form\Element\Textarea;
use Zend\Form\View\Helper\FormLabel;
use Zend\InputFilter\InputFilter;
use Zend\Mvc\Controller\AbstractActionController;
use Zend\Validator\StringLength;
use Zend\View\Model\ViewModel;
use Form\Model\Form;
use Zend\Validator\EmailAddress;


class IndexController extends AbstractActionController
{
    public function indexAction()
    {
        $json = '
        [  
            {  
                "type":"text",
                "label":"First name",
                "placeholder":"First name",
                "className":"form-control",
                "name":"first_name",
                "subtype":"text",
                "maxlength": "10"
            },
            {
                "type": "button",
                "subtype": "submit",
                "label": "Button",
                "className": "btn btn-success",
                "name": "button-1511804098888",
                "style": "success",
                "value": "Apply"
            }
        ]';


        $actionUrl = $this->url()->fromRoute('formApplication');

        $form = new \Zend\Form\Form();
        $form->setAttribute('method', 'post');
        $form->setName('test_from');
        $form->setAttribute('action', $actionUrl);
        $inputFilter = new InputFilter();

        $elements = json_decode($json);
        foreach ($elements as $element) {

            switch ($element->type) {


                case 'text':
                    $textElement = new Text($element->name);
                    $textElement->setAttribute('placeholder', $element->placeholder);
                    $textElement->setAttribute('class', $element->className);
                    $form->add($textElement);

                    $validators = [];
                    $filters = [];

                    if (isset($element->maxlength)) {
                        $maxLengthValidator = new StringLength();
                        if (is_int($element->maxlength)) {
                            $maxLengthValidator->setMax($element->maxlength);
                            $validators[] = $maxLengthValidator;
                        }
                    }

                    $isRequired = false;
                    if (isset($element->required)) {
                        $isRequired = true;
                    }
                    $inputFilter->add([
                        'name' => $element->name,
                        'required' => $isRequired,
                        'filters' => $filters,
                        'validators' => $validators,
                    ]);
                    break;
                case 'button':

                    $subType = $element->subtype;

                    switch ($subType) {
                        case 'submit':
                            $submitElement = new Submit($element->name);
                            $submitElement->setAttribute('class', $element->className);
                            $submitElement->setAttribute('value', $element->value);
                            $form->add($submitElement);
                            break;
                    }
                    break;
            }

        }

        $form->setInputFilter($inputFilter);


        if ($this->getRequest()->isPost()) {
            $postData = $this->getRequest()->getPost();

            $form->setData($postData);

            if ($form->isValid()) {

                $validData = $form->getData();

                var_dump($validData);

                die ('valid');
            } else {
                var_dump($form->getMessages());
                die('not valid');
            }
        }

        return new ViewModel([
            'form' => $form
        ]);
    }
}