The display format for dates in Lightroom is controlled by the operating system's regional settings, not by some setting in the camera.
If you are on Windows go to the control panel and look at the Clock, Language, and Region section. You can change the date format to something else and Lightroom will pick it up. For example, I just changed mine to yyyy-MM-dd and that is properly reflected in Lightroom after restarting the app.
I imagine it is similar on a Mac.
Neil