Philosophically speaking, since there is essentially no way of knowing up front what dose will work for any individual, does the individual's weight or age is (except for the under-twenty crowd, of whom there are fortunately not enough to do a definitive study anyway) really matter?

The only thing I can see is that it might affect the maximum safe dose, but even that seems to vary by individual as much as anything else. It seems to me that try-it-and-see-if-it-works will be the result, anyway.