'Retrieve original value and check it wasn\'t signed more
than max_age seconds ago.'

def unsign(self, value, max_age=None):

    result = super().unsign(value)
    (value, timestamp) = result.rsplit(self.sep, 1)
    timestamp = baseconv.base62.decode(timestamp)
    if (max_age is not None):
        if isinstance(max_age, datetime.timedelta):
            max_age = max_age.total_seconds()
        age = (time.time() - timestamp)
        if (age > max_age):
            raise SignatureExpired(('Signature    age    %s    >    %s    seconds' % (age, max_age)))
    return value
