That’s impressive. Several old versions would equal maybe 4-5-6 years? And you’re still rock solid stable? That’s pretty good.
I tend to do full OS wipes and fresh installations of my DAWs every 18-24 months these days, Mac, Win, Linux, sometimes even more often depending on several factors. It’s a bit aggressive compared to some other people, but it works for me, and my DAWs are very stable. I have found that if I wait much longer, like around 3 years, things start breaking or giving headaches… some dependency, some plugin, some driver, some major OS update, etc., will inevitably give me some hassle.
In your case, if you are still happy with your your system’s stability, there’s no harm leaving older versions installed, except for using up space… BUT if you uninstall them, there are typically few, if any, problems… you should be mostly okay.
HOWEVER, if you aren’t careful when you uninstall the old apps/plugins, you might run into a few wrinkles or even bad headaches, especially if an older version installed a sample library, for example, that is not included in a newer version, or if some older project of yours used a prior version of a plugin that you’ve uninstalled.
So just do a good inventory of the plugins and libraries that you absolutely need before uninstalling anything.
And I’d suggest whatever you do, make sure you’re doing really good backups just in case something happens that might cause you to pull your hair out.