The first time I found out about Kate before reading comics I thought she's younger than Barbara because Barbara looks like she's in the late twenties, early thirties, and it's not weird to me because I imagine Kathy as Bruce's Batwoman while Kate is the next-gen Batwoman for Dick's Batman. This was before they're made cousin, of course, and I thought it was a retcon that Babs was made younger while Kate's older.