I tried installing Lightroom 5 on my new Macbook. When I try to open it, it says Lightroom catalog named "Lightroom catalog" cannot be opened because it is too new to be used by this version of lightroom. Would you like to select a different catalog?
I'm not sure what to do.
Lightroom catalogs are not backward compatible.
You must at some point have had version 6 or CC installed.
The catalog you're trying to open has been created in Lightroom 6 or CC, and can not be opened in version 5.
I had a trial version of CC installed. What if I just want to start fresh and not open any old photos. Can I do that or do I have to buy the new version?
You should be given the option to create a new catalog, which will let you start from scratch.
Just be aware that any edits you have done to your photos in CC will not be visible - you have to start over with your work.