Just fair warning, I don’t have any hands on experience with ballistic armor, so this is cobbled together from basic research I’ve had to do over the years.
For Kevlar, I’ve been told the rule of thumb is roughly 6 months for a vest. Moisture and UV exposure result in deterioration, so as body armor this stuff has a fairly short lifespan. (It’s worth mentioning, this might only apply to the Zylon based ballistic armor that was popular in the late 90s and early 2000s, and not Kevlar armor.)
Kevlar is just a polymer fabric, so there isn’t really anything to replace. You just need to swap out the whole vest. Soft ballistic armor is also single use. Once it’s taken a bullet, it’s time to toss it and get a fresh one.
Ceramic inserts should be good until they break. Strictly speaking, ceramic armor can refer to steel or ultra-high density polyethylene, though it’s called “ceramic.” Either way, replacement plates are available for sale, and swapping out plates is easy enough. Once the plate itself is broken, there’s basically nothing you can do with it except replacement.
With stab vests, I’m honestly a little unsure. I don’t know what’s in them. If it’s just a different Kevlar weave, or a metal mesh interwoven with a polymer fabric. Either way, you’re probably looking at another case of replace after use.