These are the names of fields that are added automatically when enabling editor tracking on a feature class. Is there a reason that those fields already exist on your feature layer? Did you have Editor Tracking enabled at any point in time on the source feature class?
This is actually a known issue:
If the editor tracking fields (Creation Date, Creator, Last Edit Date, Editor) are present in a hosted feature service, Track Edits cannot be enabled on the feature service in ArcGIS Online.
NIM102295: If the editor tracking fields (Creation Date, Creato..
You could create a copy of the feature class which is the source for this feature layer and remove these fields and then republish the feature layer. Then the Editor Tracking should be successfully enabled via the Item Details.
Another workaround could be to enable the Editor Tracking on those specified pre-existing fields through ArcGIS for Desktop in the feature class properties > Editor Tracking tab and then overwrite the service. With this method the "Keep track of who created and last updated features" should already be enabled.
Please let me know if you have any further questions.