'Checks if activation key is expired.
Returns ``True`` when the ``activation_key`` of the user is expired and
``False`` if the key is still valid.
The key is expired when it\'s set to the value defined in
``USERENA_ACTIVATED`` or ``activation_key_created`` is beyond the
amount of days defined in ``USERENA_ACTIVATION_DAYS``.'

def activation_key_expired(self):

    expiration_days = datetime.timedelta(days=userena_settings.USERENA_ACTIVATION_DAYS)
    expiration_date = (self.user.date_joined + expiration_days)
    if (self.activation_key == userena_settings.USERENA_ACTIVATED):
        return True
    if (get_datetime_now() >= expiration_date):
        return True
    return False
