Have him send you a .idml file, and don't expect perfection in the conversion. A PDF of how it looks to him would be a good idea, too.
If you expect to work seamlessly with this other person one of you is going
to have change the way you're working.
I'm not sure what you mean Bob.
We were working seamlessly until my partner switched to the cloud. Usually software will open an older version with a warning of what may be missing. No warning shot was fired here, I was torpedoed.
If you have to work with someone in the cloud you have to work at least with CS6 and ask him to work with CS6 which is able to get from the cloud and which is available to get as buy version.
If he insist to work with CC (a lot of reasons are given) you have to go to the cloud too.
The exchange of InDesign files as IDML is not very recommandable as there a lot of changes in the layout after converting and opening in the other version.
Yes, InDesign is opening an older version's file but not a newer version's file and that is the problem you are running in.
You were torpedoed by your co-worker, not Adobe. Take it up with him.
At some point, however, you're not going to have a choice but to upgrade.