To delete files, you should use /2/files/delete_v2 or /2/files/delete_batch.
Those require you to specify exactly which files to delete. To first find files any/all files with modified datetimes older than a certain date, you can use /2/files/list_folder[/continue]. Those allow you to list the metadata for all files and folders under a certain path. The returned metadata will include both client_modified and server_modified. Click through the "Metadata" documentation there for more information on the returned metadata fields.
By the way, those are links to the documentation for the HTTPS endpoints themselves, but we recommend using one of the official SDKs if possible. Those have corresponding native methods for the HTTPS endpoints.
