This is basic "mind palace" theory, no? Human memory is linked to navigation; the more you associate memories with navigable places, the stronger your memories will remain.
what's weird is that even while I still use my representations formed as a kid, I don't seem to make new ones when I learn new info, which makes remembering things much harder.
I do the exact same thing! I wrote a blog post about how I visualise numbers: https://bjoernkw.com/2022/01/02/i-see-numbers/
It's a specific type of synaesthesia called "time-space synaesthesia".
Very interesting; why do you think that is?
Some of us have a location synaesthesia where thinking about particular topics often evokes a sense of being specific places, looking particular directions, each paired apparently randomly (but durably) with topics. Not sure if this is association (since it seems to form without any associating event with the location) or just signal "leakage" triggering the connection.