<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 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]