Since your mystery plant has striped leaves, it's for sure not the same species as the 6-ft. tall one I mentioned, which is also a volunteer. But could yours reach 6 ft. tall? No idea. Doubtful the striped-leaf volunteer plant I found earlier this year has reached 6 ft. tall because if it had, I wouldn't be having a hard time locating it again. Could it be from being in mostly shade, or that it's just not a tall species? IDK. If someone is able to recognize the species of yours, you can know what its' potential is.
