I’d say O-8 or higher based on this chart:
O-5 with 28 years here...mine is close to the amount mentioned.
O-4 with 22 so I must be thinking numbers associated more with my era as I retired in ‘87, and the chart left me wondering if it reflected time in grade or time in service, as I believe the last number on top was 8 which appeared to to be unrelated to reality. At any rate, I’m grateful I was able to retire as not everyone who serves is afforded the opportunity, and I was payed well for doing what I loved.