Oh, I'm definitely of a "certain age", but I'd doubt that you could actually be specific about that. Hogwash is a term, that to me, means watery shit. When you wash of a dirty hog that is exactly what you get. That said I don't think I knew any adults growing up that actually said it, I'm pretty sure I learned it from TV or reading.
So far as our brains processing all of reality goes, that is an impossible feat for our brain, or any other for that matter. We certainly seem to be capable of processing the laws that determine interactions of mater and energy and that is all that actually matters. The current knowledge isn't perfect and of course might take eons or days to advance significantly. And it is impossible to know how much we don't know. But there is no point of fact that I've ever heard of that indicates we're missing something fundamental, possibly with the exception of dark matter.
Ohh look a fun part:
I can tell by your pejorative use of the word "scientism" that you're the embodiment of a non-sequitur. Everything is reducible and quantifiable through science. We may not have the means or ability as of yet to do so, but we'll get there eventually. To argue for something being permanently beyond science is to argue that it is beyond reality, and if it isn't a part of reality than it literally doesn't matter.