With a solidworks subscription licensing, am I able to install older version Solidworks?
yes. Backwards compatibility. Not forwards.
I would say it depends on how old, and if you have the desired version available. If you do not have the older version available there are a limited set of versions on the site to down load. After that your VAR "should" have older versions available and they should be able to help you.
Last I check, I can get down to 2017.
I believe you should be able to load older versions from the newest that your subscription allows, back as far as your hardware will allow - but only on the same system (you can not have the same license on multiple machines).
You should also be able to load multiple Solidworks versions (not sure about service packs) as long as they are different year versions and with the same restrictions as indicated above.
However, not having done it (loading an older version when you already have a newer version) you could have problems.
You want to be sure the templates and settings ... are separate for the different versions or you will have compatibility issues. and don't save new version templates over older version templates if you want to run the older version software with those templates.
I suggest you do a backup of your drive (ghost the drive) before doing this incase something doesn't work.
Retrieving data ...