I am working for SCDOT on a project and I have created different personal geodatabases for highway crashes for each year, also I have created a separate personal geodatabase for the network (routes). Each crash has a LRS (linear referencing) field that needs to be related to the LRS field in routes network. Apparently, Create Relationship Class does not work to relate two separate geodatabases. Is there any other solution for that?
He just meant that the Personal Geodatabases (*.mdb) are not supported with ArcGIS Pro.
This does not matter for you, if you are using ArcGIS Desktop as it is a 32-Bit application.
ESRI is moving more and more to Pro as their recommended desktop app (IMHO - not yet a replacement for Desktop though), as that is where they are placing most of their development resources. Pro is a 64-bit app and personal geodatabases are not supported in a 64-bit environment. Just information to plan for the future with your GIS architecture.
Check if "Relates" suits your needs:
Relates defined in ArcMap are essentially the same as simple relationship classes defined in a geodatabase, except that they are saved with the map instead of in a geodatabase.