Lambda functions that have DynamoDB or Kinesis Streams as their event source read from those streams with an iterator. If DynamoDB is changed or records are put to Kinesis too rapidly, your function may not be able to read from the iterator quickly enough. This is reflected in the iterator age, which is the amount of time between when a record is written to the stream and when Lambda reads it.
To troubleshoot an anomalous iterator age, first, check if the code triggering changes in your stream are erroneously doing so at an increased rate. If so, fix the code that’s causing the issues and just wait for Lambda to catch up. Otherwise, you will have to increase the concurrency on your function so you can invoke your function more and lower the iterator age.