In the past, when I wanted to delete system generations older than 7 days, I’d run:
nix-collect-garbage --delete-older-than 7d
I’m in the process of switching my config to flakes and getting up to speed on using the new nix command, and it looks like the replacement for nix-collect-garbage is nix store gc, but how can I get it to delete system generations older than some specified age?