I remember well seeing 20 year E-3's retire! 30 year E-5's!
I gave the USAF a six year first term enlistment, and for my sin, I put on E-3 two weeks before I graduated basic. Gave me the same rank as the assistant T.I. THAT was interesting! Also ended up putting on E-5 under three years, which for the time in the AF, was unheard of. Made me a Minuteman missile maintenance team chief, and my assistant was an E-4 with 14 years in. It helped a bunch that he was an outstanding troop, and covered my butt more than once while I learned the ropes of management!
I heard that he retired with 32 years as an E-9.
Jimmy Carter, that spineless slimeball, made my mind up that I'd had enough. Should've stuck it out, but my last three COLA's went into my BAQ, and I was living on post with my family, so my raises went onto the LES on one column, and out in another. Finances were stretched just a mite! Declined the E-6 tests/board, and split the program. Went into the National Guard the day after my ETS, and gave them another 11 years, but every time I was up for E-6, I had a PCS on my civilian AF job, and ended up being one of those 17 year E-5's.
My son in law was an E-6 with a primary MOS as a combat medic. Went to school, got his degree, went to OTS, and is now an O-3 nurse. He also, was having trouble making it to E-7 and sideslipped the enlisted promotion boggle and went the officer route. Something to consider.........