E6 in 3 years? Is there such thing as making rank too soon?

no not at all especially if you know what your doing and can save lives. i went to nam as a private and came back as an e-5 buck Sargeant. i save some lives i know of. then six months my commander official put me in for e-6 staff Sargeant. i made the rank. i did make some dumb mistakes, that i learned from, but no one got hurt or confused, i just pissed this captain off. no worries though, he wasn't the best official. i kinda wished i had stayed in the army, but i wanted to live my life as i wanted. a 50/50 decision.

Not really. I knew an E-6 when I was in Germany. First met her in 1990. Don't remember when she got promoted, but she went to ANOC the same time I went to BNOC which was in 2000.

Yes, Sir there is.
Sometimes, and it is up to the leader to figure it out, a person meets every published metric to be promoted but just does not meet the landing gear to the tarmac ability. This is where it becomes a critical skill to be able to vocalize and put into words the "WHY" you as a leader just do not feel comfortable promoting someone right now. Perhaps they are not mature enough, or they demonstrate a propensity to complain or seek self over unit.
Malcolm Gladwell wrote a book called "Blink" I highly recommend it. Just Sayin'

You were lucky I got to third class petty officer but that was it in the four years I was in the Navy. I never got into any trouble while in. If I would have gotten to 2nd class I would have stayed in longer.

I have never seen a fast tracker that was worth anything, at least not in my MOS, but there are many variables that have to be taken into account. First maturity, if you can't take the job seriously and be responsible for yourself and your troops, you are a no-go at that station. Second, administration; counseling packets, reccomendations/nonreccomendations for promotion or board, primary maintenance checks and services, precombat checks and inspections, drill and ceremony, pretty much the total NCO and Soldier package. Third Military Occupational Specialty; do you know your job at your level and one level above you? If not you are failing yourself and your unit. Many fast trackers have the first two, but not the third through no fault of their own; job experience takes practice, and after Desert Storm until the Iraqi campaign (1996-2005 approximately), there were many jobs in the army that were contracted out to civilians on American bases, so there were many NCOs in my unit in 2003 that had no clue how to do their jobs when we got to Afghanistan. It is not being technically proficient when the E4 who was Marine Corps prior service has to teach their boss how to do the MOS based tasks.

About the time I was at the end of my enlistment, we (The Corps) acquired "leadership" that had a stated policy that no one would make E5 on their first enlistment. Didn't matter if it was 2, 4 or an extension to 6 years. No one would make E5 on their first enlistment, ESPECIALLY in the Air Wing.

It was immediately post-Vietnam, the civilian aviation industry was ramping up, and of course, the MCAWs emptied out with all possible speed.

TBH, I enjoyed my time in The Corps but not enough to give up twice the money, half the hassles, and no complaints about my wife's "attitude" to return at the same rank I had left.

The same can happen with officer ranks. During the height and later part of the Viet Nam War a 2LT would get promoted to 1LT in one year which is OK but then the person would make CPT in another year. When I was at Infantry Officer Basic Course at then Ft. Benning there were guys in my class who had been commissioned ar 2LTs and then got a deferred entry to go to graduate school for 2 years but their time in grade clock was still ticking. So, they had the potential of going to Viet Nam as a Company Commander with no actual unit active duty experience. I don't know if any of them did but it was a possibility. I went in as a 2LT and got promoted to 1LT during my first weeks as a Platoon Leader in Viet Nam.

Those who are focused and have found their Nitch, deserve to be promoted. This also makes them more noticed by their superiors to be groomed for OCS. They can take the CPO examen 1 year sooner and pass that qualifies them for OCS, Which is also great for the military.

I think it depends on the MOS and volume of work. I was an E6 at 24 years old (turned 20 in basic training), however, I was in a fast promoting CMF and volume recruiting. Meaning we had 18 year old recruits coming in all the time. If I passed on the promotion or the opportunity to be on the EPS list it just meant someone else would step up. Senior Leaders should understand their younger leaders and develop ways to motivate so to get the best performance out of everyone.

Depends...in combat it's understandable for exemplary leadership, not in combat then it's way too fast. Makes you wonder...