You could use a script by Jongware to make sure what version the file is:
[Ann] Identify Your InDesign File
There is also "Soxy" by Rorohiko that would exactly do what you like:
That doesn't help them "open" the file in the last version it was created in.
Only the Soxy by Rorohiko is the only way I know of.
It's really poorly implemented by Adobe when opening files. I got a trial of CS6 and it's expired now but I haven't removed it from the computer, in case I thought I'd buy a license I just have to enter the key.
But any time I open a file from my folders it opens in CS6. Which is annoying. And even trying to overwrite what program it should open by default doesn't work either!
You can view a files History in Adobe Bridge too and that will alert you to what version of InDesign it was created in when you view the metadata
You might try my system. Go into the InDesign CS6 folder (in Applications), "zip" the application, and trash the unzipped file. It won't open any more files.
Then when you need to use CS6 again, double-click the zipped file. (The zipped version stays there, so you just delete the unzipped file when you're through with it again.)