I need help to undertand "GET <target>/_ilm/explain" output for ILM policy phases moving

[LizardNerd]

Hi there, I'm fairly new to Elastic Stack. I created an ILM policy for my first data stream, then I ran:

GET .ds-logs-pfsense.log-default-2023.01.26-000004/_ilm/explain

This is the output:

{
  "indices": {
    ".ds-logs-pfsense.log-default-2023.01.26-000004": {
      "index": ".ds-logs-pfsense.log-default-2023.01.26-000004",
      "managed": true,
      "policy": "opnsense",
      "index_creation_date_millis": 1674756268079,
      "time_since_index_creation": "49.62d",
      "lifecycle_date_millis": 1676052317681,
      "age": "34.62d",
      "phase": "cold",
      "phase_time_millis": 1678644702198,
      "action": "complete",
      "action_time_millis": 1678644702398,
      "step": "complete",
      "step_time_millis": 1678644702398,
      "phase_execution": {
        "policy": "opnsense",
        "phase_definition": {
          "min_age": "30d",
          "actions": {
            "allocate": {
              "number_of_replicas": 0,
              "include": {},
              "exclude": {},
              "require": {}
            },
            "set_priority": {
              "priority": 0
            }
          }
        },
        "version": 3,
        "modified_date_in_millis": 1678300649074
      }
    }
  }
}

I need a clarification with the parameters "age" and "time_since_index_creation".

The doc say this (Explain lifecycle API | Elasticsearch Guide [8.11] | Elastic):

The time since the index creation (used for calculating when to rollover the index via the max_age)

The age of the index (used for calculating when to enter the next phase)

So, what is the difference between "age" and "time_since_index_creation"?
Which one do I need to consider to know when my index will pass through ILM policy phases?
Why "age" and "time_since_index_creation" values are different in my case?

Thank you, kindly be patience, I'm new.