Symfony2 OverAge Validator

Entity

<?php

namespace Acme\Entity;

use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Validator\Constraints as Assert;
use Nmn\Validator\Constraints as NmnAssert;

use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;

/**
 * @ORM\Entity
 * @ORM\Table(name="my_table_name")
 */
class MyEntity
{
    /**
     * @ORM\Column(type="datetime")
     * @Assert\DateTime()
     * @NmnAssert\OverAge(age="18")
     */
    protected $dateOfBirth;
}

OverAge

<?php

namespace Nmn\Validator\Constraints;

use Symfony\Component\Validator\Constraint;

/**
 * @Annotation
 *
 */
class OverAge extends Constraint
{
    public $message = 'The minimum age required is {{ age }} years';
    public $age     = 18;
}

OverAgeValidator

<?php

namespace Nmn\Validator\Constraints;

use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;
use Symfony\Component\Validator\Exception\ConstraintDefinitionException;
use Symfony\Component\Validator\Exception\UnexpectedTypeException;

/**
 * 
 * @api
 */
class OverAgeValidator extends ConstraintValidator
{
    public function isValid($value, Constraint $constraint)
    {
        if (!$value instanceof \DateTime) {
            throw new UnexpectedTypeException($value, 'DateTime');
        }
                
        $minimumDate = new \DateTime(date('Y-m-d'));
        $minimumDate->sub(new \DateInterval('P'.$constraint->age.'Y'));
        $interval = $minimumDate->diff($value);
        
        $dayDiff = $interval->format('%R%d'); 
        
        if ($dayDiff > 0) {
            $this->setMessage($constraint->message, array('{{ age }}' => $constraint->age));            
            return false;
        }
        
        return true;
    }
}