code: def age_simulants(self, event: Event):
          
          population = self.population_view.get(event.index, query="alive == 'alive'")
          population['age'] += event.step_size / pd.Timedelta(days=365)
          self.population_view.update(population)
docs: Updates simulant age on every time step.
  
          Parameters
          ----------
          event :
              An event object emitted by the simulation containing an index
              representing the simulants affected by the event and timing
              information.