Do you think there's certain age gaps that are wrong or is that all relative?

I've heard things like its wrong if a 39 year old and a 19 year old date but its perfectly fine if a 22 year old and a 19 year old date. I know the age gap is bigger but I don't know exactly what that even mean. Maybe its not common to see bigger age gaps and it can throw people off but a lot people make assumptions that certain age gaps are wrong.