code: def _won_in(self):
          
          if not self._summary['finished']:
              return
          starting_age = self._summary['settings']['starting_age'].lower()
          if starting_age == 'post imperial':
              starting_age = 'imperial'
          ages_reached = set([starting_age])
          for player in self._summary['players']:
              for age, reached in player['ages'].items():
                  if reached:
                      ages_reached.add(age)
          ages = ['imperial', 'castle', 'feudal', 'dark']
          for age in ages:
              if age in ages_reached:
                  return age
docs: Get age the game was won in.