[aosaigh]

I do this with my Downloads folder using Hazel[1]. I have an “Archive” folder split into subfolder of screenshots, pdfs, videos etc.. After a month in the downloads folder, Hazel moves everything into the Archive subfolder automatically, sorted by year and month.

[1]: https://www.noodlesoft.com/

[gcanyon]

Yep, I've been recommended Hazel before, but I like the control I get with the AppleScript. In particular I like the higher cadence of sweeps, mine does my desktop, downloads, and documents folders, and mine will ignore a file if it has a label, so I can easily keep things if I want.