New player who keeps on poking holes into my world economy

[KorvinStarmast]

Just a thought, but without mentioning any specific details for many thousands of years societies *did* run, worldwide, on the assumption that magic was real and required meaningful government policy to utilise or defend against. Saying a magic using society couldn’t look anything like our own, runs into trouble if you consider, e.g., witch hunts. And it’s not that this was an assumption of low magic either, we’re talking raising storms and sinking entire fleets.

That rarity and danger is a part of where the whole Cthulhu (and the CoC game) start, isn't it?

Point out that the fantasy world has elves that live for hundreds, if not thousands of years, and have their own currency. Why would anyone pay extra for an 80-year-old coin when the elf who came through town just paid for his lunch with a 300-year-old one?

Good point.

I'll take that a step further: The "it's worth more to a collector" may be true, but the 80 year old quarter still spends like a quarter. I used to work as a cashier (in the 70's, high school job). I would now and again get silver coins in change / payment, and I'd (as often as I had loose change in my pockets) swap them out for non-silver all the time. Had a collection of over 80 of them, pre 1964 dimes and quarters, that were part of what got stolen from my apartment during a break in (late 80's). The initial premise that the "economist-player" asserted is somewhat flawed for a variety of reasons, and one is that there is by default a market for coins older than X years.
That is entirely a world building matter for the DM (or an anachromism imported from our modern world to their game world as the clock on Bilbo's mantle was).