Q: Why doesn’t Curator 4 work with older indices?

The actual error message might look something like this:

2016-08-30 13:18:37,702 WARNING Index: indexname has no "creation_date"! This implies that the index predates Elasticsearch v1.4. For safety, this index will be removed from the actionable list.

Older indices (made before Elasticsearch 1.4) do not have this metadata. Trying to support this in Curator 4 would result in having to catch edge cases for some indices, but not for others. In order to keep the code clean, and with fewer exceptions, a design decision was made to not work with indices without a creation_date. Curator will not change them in any way, ever. They are automatically removed from the list of actionable indices.

You can use the Sense plugin for Kibana to act on these indices manually, or your preference of API method.