Yes you are right - rclone only filters on file ages.
Rclone makes some attempt to return directory ages but it isn’t that reliable among cloud storage providers…
I’d probably do this by naming the directories YYYY_MM_DD
then use a bit of shell script to find when you have more than 30. rclone lsf
is ideal for this kind of scripting…
So something like find the oldest directories more than 30
rclone lsf --dirs-only . | egrep '^[0-9]{4}-[0-9]{2}-[0-9]{2}' | sort -r | awk 'NR > 30'
you can then take this list and use rclone moveto
to move them an Archive folder.