code: def _reduce_age(self, now):
          
          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]
docs: Reduce size of cache by date.
  
          :param datetime.datetime now: Current time