code: public void addFamilyWithMaxAgeRule() {
      System.out.printf("%nCreating column family %s with max age GC rule%n", COLUMN_FAMILY_1);
      // [START bigtable_create_family_gc_max_age]
      // Creates a column family with GC policy : maximum age
      // where age = current time minus cell timestamp
  
      // Defines the GC rule to retain data with max age of 5 days.
      DurationRule maxAgeRule = GCRULES.maxAge(5, TimeUnit.DAYS);
  
      // Creates column family with given GC rule.
      try {
        // ModifyColumnFamiliesRequest can be used both for adding and modifying families, here it is
        // being used to add a family
        ModifyColumnFamiliesRequest columnFamiliesRequest =
            ModifyColumnFamiliesRequest.of(tableId).addFamily(COLUMN_FAMILY_1, maxAgeRule);
        adminClient.modifyFamilies(columnFamiliesRequest);
        System.out.println("Created column family: " + COLUMN_FAMILY_1);
      } catch (AlreadyExistsException e) {
        System.err.println(
            "Failed to create column family with rule, already exists: " + e.getMessage());
      }
      // [END bigtable_create_family_gc_max_age]
    }
docs: Demonstrates how to create a new instance of the DurationRule.