Como criar um modelo Django que herde de classe pai como proxy, com restrições na consulta

models.py

class Person(models.Model):
    first_name = models.CharField(max_length=30)
    last_name = models.CharField(max_length=30)
    age = models.PositiveIntegerField()

    def __str__(self):
        return self.first_name


class Majority(models.Manager):
    def get_queryset(self):
        return super(Majority, self).get_queryset().filter(age__gte=18)


class MajorityPerson(Person):
    class Meta:
        proxy = True

    objects = Majority()

    def __str__(self):
        return f'{self.first_name} {self.last_name}'

    def clean(self):
        if self.age < 18:
            raise ValidationError('It cannot be under 18 years.')