A name that will date is one that is very popular, eventually wanes as people inevitably tire of it and move onto something else, leaving those with the name to be associated with that era.
So names like Claire, Joanne, Karen, etc for my generation.
This generation's very popular names are all the Milly, Tilly, Lilys, Ava, Isla, Ruby, Daisy, Olivia, Isabel/le/las, Ellie, Harry, Charlie, Alfie, Archie, Jack, Sophie, Evie, etc, etc.
All nice names, but very popular and of-the-moment.