its almost 2023 and over 10 years since bayou arc and kaine still stuck at 5000 commander
chu new gen reached general offscreen years ago
zhao absolutely has no young talent
Setting aside the fact Kaine has never stated an interest in climbing up the ranks, her priority is Ri Boku's safety and wellbeing. She desires to be close to him at all times. Since her introduction she has functioned more as an aid like Ma Ron, also a 5K Commander (and likely has had a much longer career based on age), only she can and will fight. Kaine is not stuck, she is exactly where she wants to be .
That said, the Zhao do have young and talented generals Fu Tei is the same age as the Q3 and he's a general, Hara just hasn't done much with him. Shun Sui Ju is in his late 20s to very early 30s, somewhere around 28-31, so he would be counted among the same generation given that Shin should be about 26-27 by now and Mou Ten and Ou Hon are 27-28.
The Zhao probably would've had more young talent but their wars with Qin diluted the talent pool quite a bit. They lost 400,000 military-aged (AKA breeding age) men not that long ago, and who knows what the total is when adding up the casualties before the massacre that ended the war.
Why new talents when you can pull top tiers general out of your ass after every defeat?
People complain about this as endlessly as they do about "plot armour" - do you people actually want to be entertained? The history isn't exactly exhaustive on notable officers and generals. It's either this, or the manga loses a lot of interesting characters and characters as you know them.