older versions

Direct Download Links https://prodesigntools.com/tag/ddl MAY help
-you MUST do what it says in Note: Very Important Instructions
-https://prodesigntools.com/adobe-cc-2015-direct-download-links.html#download-instructions
-the prodesign links go directly to Adobe's file server, so this process will
--only work until Adobe completely removes the old version(s) from the server
.
IF/When you do have a download, be sure to copy it to AT LEAST one external device
-since Adobe does sometimes remove old versions from the server
-a usb flash drive or external hard drive, or write to a DVD

No, not from Creative Cloud desktop app.  Adobe expects customers to use the latest software, no more than 2 versions back.

You need Win10 (1903 or higher).

Please ensure your computer meets or exceeds the minimum system requirements to run Creative Cloud + OS + all other apps you use. Check each one.
- https://helpx.adobe.com/creative-cloud/system-requirements.html
- https://helpx.adobe.com/after-effects/system-requirements.html