Symfony2 inherit_data issues and workaround

NameType.php

<?php
class NameType extends \Symfony\Component\Form\AbstractType
{
    public function buildForm(\Symfony\Component\Form\FormBuilderInterface $builder, array $options)
    {
        $builder->add('firstName', 'text');
        $builder->add('lastName', 'text');
    }
}

Person.php

<?php
class Person
{
    public $firstName;
    public $lastName;
    public $age;
}

PersonType.php

<?php
class PersonType extends \Symfony\Component\Form\AbstractType
{
    public function buildForm(\Symfony\Component\Form\FormBuilderInterface $builder, array $options)
    {
        $builder->add('name', NameType::class, ['inherit_data' => true]);
        $builder->add('age', 'integer');
    }
}

User.php

<?php
class User
{
    public $firstName;
    public $lastName;
    public $email;
}

UserType.php

<?php
class PersonType extends \Symfony\Component\Form\AbstractType
{
    public function buildForm(\Symfony\Component\Form\FormBuilderInterface $builder, array $options)
    {
        $builder->add('name', NameType::class, ['inherit_data' => true]);
        $builder->add('email', 'email');
    }
}