I don't think you can put a quantifiable number like age on it. Some older students are in fantastic shape (Jhoon Rhee and Hee Il Cho come to mind). Others are 25 years old and couldn't jump if their lives depended on it. My answer is this: I will stop jumping when my body tells me it is time to stop. Otherwise, with proper practice and conditioning, I see no reason to believe I will have to stop jumping anytime soon (I'm 38).
I agree. When my body tells me to slow down then I'll take it easy. But what about advancing to the next level? Some required techniques are jumping, spinning, and jump & spin. If one of your required forms contains a jumping spin kick from the sitting position, then aren't you expected to do it in order to advance to the next level. IMO if your body is telling you not to do something then don't do it fast. But if your instructors are telling you that you need to do it in order to advance, then I guess you have choice to make. I too am 38 and am now carrying 20 extra pounds. I'm still practing my jumps/spins but just a little slower and lower...for now.