Mayberry
This is my own theory but given the posts on Bonesmart and I think it has some merit.
I think the younger you have a TKR the more difficulty and time it will take to recovery ROM and muscle strength. The reason being that if you have to have surgery in your 40's or 50's you most like had a accident, some kind of injury, a long time problem due to biomechanics or played some serious sports (think football players) or even a heavy duty hiker, runner along with a family OA history. Now with any of these situations you most likely also suffered ligament, tendon, cartilage, muscle damage and to manage the knee pain/problem your body adapts some weird walking habits which further damage all those other structures. Then if you needed surgery to correct any of those problems you have just added more stress to the entire joint. As a firefighter you certainly have a career with major knee joint ware and tear.
Compare that to someone in their late 60's or 70's who had none of the above but just developed run of the mill OA as they aged. Most people as they age are not as active so even with the OA developing they are not doing as much damage to the joint and most of that damage will just involve the bones and the articular cartilage covering them.
Now after my BTKR, I went to inpatient rehab. My first roommate was in her early 70's and came in 3 days postop BTKR and already add ROM of 108 (even the PT could not figure out what she went to rehab other than some home care issue). She was getting in and out of bed by herself (though she wasn't cleared to) and moving just fine. Now the last time my knees bent over 100 was probably 25 years ago. She stayed about 3 days and left with ROM about 115 and 0 extension. A day later came roommate #2 and she to have ROM over 100. Within 2 days she was cleared to get out of bed my herself and take walks alone. Now I had been in rehab about 6 days at that point and they would not let me get out of bed myself or going strolling and I was probably at least 24 years younger than either of them. When I left rehab after 11 days we had the left one at 104 with alot of pushing and the right barely over 100 and extension on the right still at -12. Now I had problems starting in my teens, 9 major surgeries and a slight break in the tibia due to the BTKR and surgery that went 2 1/2 times longer than planned because the OS had an awful time trying to get the implant into the right knee.
I had a great PT who looked at the entire history and knew it was going to be a long haul. He said he wanted to make sure that we had a good outcome and no complications. I really admired his patience.
Now as soon as I heard the milestone statement from the PT all my bells went off. Yes, you want to get that ROM moving to prevent scar tissue forming which can lead to a manipulation but at the same time pushing too hard causes more swelling and pain and that slows down rehab. After my first surgery I was at a PT clinic that used all these milestone markers even though I kept telling them something was wrong. The end result was a second surgery as the plica got caught under the tendon during surgery so no matter how much they pushed the knee was not going to bend. What was worse was that if they and kept going (the only thing that stopped them was the knee size increased about 4 times in less than 3 weeks) they would have probably rupture some tendons.
Well, this was a bit long winded but the bottom line is that if the PT is not listening and you don't feel comfortable with her, find someone else -- is your body and you know it better than anyone.
Good luck
SImon