I'm not sure but I just keep trying to go up in small increments. My shoulders I don't tax too much but my back/hips I'll work on harder. I bought 20lb weights after a year and use them for rows and a single tricep move. I can't use them for any other move yet but working on chest for a few. I can't see me going higher than that at this time but want to keep the bone responding. If I see improvement next year, it will motivate me to do more.
I've looked on many sites and pretty much it's what is challenging for you. If it's too easy, you aren't taxing the bones, too hard to do more than 3 or 4 reps, too heavy. They also say to use body weight also, mix it up. Also no momentum, use slower movements.
https://americanbonehealth.org/exercise/bonesense-on-osteogenic-loading/