At a glance it seems like there works be a way to form the weighting adjustment into a subquery and multiply by the reciprocal. And then it’s still multiply-accumulate, but maybe I’m missing something.
At a glance (1 / (product_age_days * age_scale_constant)) just seems like another factor you can multiply (with the calculation of reciprocal costing more in compute time). Again, I'm more than likely misunderstanding you or lacking the context.