code: func (mc MongoClient) EventsOlderThanAge(age int64) ([]contract.Event, error) {
  	expireDate := (db.MakeTimestamp()) - age
  	return mc.mapEvents(mc.getEvents(bson.M{"created": bson.M{"$lt": expireDate}}))
  }
docs: // Get Events that are older than the given age (defined by age = now - created)