At what rank should Soldiers be exempt from organized PT?

No rank should be exempt lead by example

Sigh. I remember the days of very rotund NCOs and Officers in the late 70s. Especially the "Mess Sergeant". I rather liked them as they might stop a bullet while I shot from behind them as cover. The stereotypes in Beetle Bailey were not that far off the mark.
Now, if current PT really proved combat readiness, I'd still be leading PT. As it were, I led the run and martial arts, which made much more sense to me. I've never been a fan of testing by age group, yet as I got older in the Army, it was tough to run in the front--yet I did for as long as possible, then retired when I could not.
Just as we have many sizes of hats and shoes and gloves and jackets, one size of PT does not fit all people and all units.
I am a fan of a very basic fitness test that measures the middle. Then add a level that proves you are a soldier and can move, shoot, and communicate with your particular unit. The real PT = Physical & Tactical test.

Any rank above PL and PLT SGT, which doesn't mean it's optional, it just means you have more important things to than PT with the troops. Our older Major could run with the best of them...so I didn't need him out in front, but I did want to see my LT sweating with the rest of us.

All ranks should be doing PT as a group. Now schedules and positions may prevent the SM from being at every organized PT but the higher the rank the more beneficial it is for the unit. I have seen some of the best and motivated PT being done with my Soldiers when the battalion commander makes an appearance at the units PT. I have seen MG Wyche appear in formations at random and conduct PT as a regular Soldier. Lead from the front and set the example.

I have been exempt from organized PT. But I was also training for a marathon and needed to do training runs which lasted longer than the allotted time for PT. I think it's a case by case situation. I believe everyone should participate in some way. The senior leadership in my unit almost always participates in organized PT unless restricted by profile.

It seems that my question was vaguely phrased. Organized PT is something everyone should be involved with; hence the word "organized". What I meant was that it is incumbent on a leader to be intrinsically motivated and they should therefore not be micromanaged, especially in PT. In my opinion, organized PT should only be conducted once or twice a week at the Company or Platoon levels at most. Squad Leaders (SSG/E6), Team Leaders (SGT/E5), and above should manage their own squads and teams, as they are the ones directly responsible for the good, bad, and indifferent of their Soldiers. As far as seniors are concerned, I believe that unless they hold a leadership role—in this case, a Platoon Sergeant, then they should be able to do as they see fit for PT. Most would agree that training is more effective at the lower levels. Additionally, if a Soldier at the NCO and above level can’t maintain the standard in the most basic of Soldiering tasks, i.e., PT and adherence to the ABCP, then they should simply be chaptered. Soldiers who fail to meet the standard have always been the burden that causes mass punishment, and let’s face it, forcing a Soldier who scores a 300+ or a Senior NCO do conduct Organized PT on a regular basis is borderline toxic leadership. This is not the way you foster critical thinking/thinking outside the box, self-motivation, and good leadership. It is simply perpetuating a substandard force.

No rank, should be based on PT score

At no rank should anyone be "exempt" from organized PT. Am I saying the battalion commander, SgtMaj, sections chiefs and OICs ect be out there every day? No. But seeing your higher leadership out with you once in a while once a week, month, quarter depending on circumstances is true leadership. PT is not just about getting in better shape. It also raises moral and builds comradery. Not PTing with your Marines goes against many leadership traits and principals.
Set the example
Train your Marines as a team
Know your Marines and look out for their welfare
Enthusiasm
Dependability
Loyalty
That's just a few that stand out to me. I understand that PT with your Marines is always possible, but put forth an effort to be engaged as much as possible and you will see the results in the end.

FIELD GRADE AND UP. PVT THRU CSM AND JR OFFICERS SHOULD ALL PT TOGETHER, WE TRAIN TOGETHER AND DOBATTLE TOGETHER. IT'S. CALLED LEAD BY EXAMPLE. WHEN I WAS A ISG FOR A BCT UNIT BACK IN THE LATE 80'S I DID PT WITH MY TROOPS EVERYDAY.

Never, regardless of score or rank.