docs: def birthday(self):
          """
          Return a string representing the age of the process.
          """
          if isfile(self.pid_file):
              
              # Timestamp / timezone string
              tstamp  = datetime.fromtimestamp(self.created())
              tzone   = tzname[0] 
              weekday = WEEKDAY[tstamp.isoweekday()]
              
              # PID file age / age string
              age     = self.age()
              age_str = '{}s ago'.format(age[0]) 
              
              # Birthday string
              bday   = '{} {} {}; {}'.format(weekday, tstamp, tzone, age_str)
              
              # Return timestamp / timestamp string
              return (self.created(), bday)
          return (None, None)