In short, with only the information presented in your question, you can’t.
The basic problem is that depth information is lost: a point in the image corresponds to a ray emanating from the camera center in the scene. In this case, your object could be anywhere along the ray $(18.785,-104.035,9.9124)+\mu(21.815,4.3702,-6.5432)$. You can check for yourself that your camera matrix maps this entire ray to $(521.46,224.54)$.
Having the camera matrix gets you a lot, but not this missing depth information. There are many ways to extract size and position information from an image, but they all require some known reference to get things started. For example, if you know that this object is at ground level and know the equation of the ground plane in the scene, you can find the intersection of this plane with the back-projection ray. Assuming that the object is more than just a single pixel in the image, if you know something about its size/shape/orientation, you could use that to recover its depth in the scene. And so on.