class Person(object):
    """docstring for Person"""
    def __init__(self, name, age):
        super(Person, self).__init__()
        self.name = name
        self.age = age

    @property
    def age(self):
        print('old enough')
        return self.__age

    @age.setter
    def age(self, value):
        if value < 21:
            raise Exception(f'{self.name} is not old enough.')
        else:
            self.__age = value