Partially answering my own question, it looks as if the reduction in weight standards from "over age 40" to "over age 50" is 12%, and from "over age 50" to "over age 60" is 25%. I wonder what the methodology is-theoretical, empirical or what?
My interest is personal and practical; I am "over age 70", and like to screw around with the numbers.
Clearly, this not a step-wise progression, and is probably some sort of curve, but that looks steep to me. anyway, if any of you have any ideas about these calculations, there are are plenty of little old guys out there who are interested.