def _reduce_age(self, now):
        """Reduce size of cache by date.

        :param datetime.datetime now: Current time

        """
        if self.max_age:
            keys = [
                key for key, value in iteritems(self.data)
                if now - value['date'] > self.max_age
            ]
            for key in keys:
                del self.data[key]
Reduce size of cache by date.

        :param datetime.datetime now: Current time

        
robobrowser/cache.py