Can I edit website created in an older version of DW in DW CC?

Yes and no.

All versions of DW produce html. All versions of DW allow you to edit html. The problem comes in if you are used to certain features with dialogue windows that have been removed from the program. Over the years, there have been a few. If you have a function you use often that has been removed/replaced, you won't have access to the dialogue windows that you are used to seeing to modify the underlying code anymore.

DWCC2017 will still allow you to edit anything you want, but the dialogue windows for deprecated features won't be there.

Either way, you should still be able to hang onto your old version if needed, during the transition. When installing DWCC, make sure to click the Advanced Options link in the installer dialogue. That will allow you to turn off the "Remove Older Versions" option and should allow you to have both your legacy version and the most current.