Answering a Grammar Nazi

It's not really a slang or usage issue. If it's in the context of "(some of) us old people...." then it's being used as an object (here the object of the preposition "of") correctly. If it's the start of a sentence (meaning as the subject) then it's we (the basic sentence being "We relate.")

And where exactly did YOU do DOCTORAL-LEVEL work in English linguistics?

It's the same thing as "Me and John are going to the movies tonight." SPOKEN CONVERSATIONAL language is ALWAYS **very** different from "formal" language, and ESPECIALLY "us old folks" is OFTEN used in American SPOKEN English, even by people with related doctoral study.

Of course, GRAMMAR NAZIS just don't get that!

Oh sorry for only taking classes at the Master's level your highness. Citing informal vs formal shows you don't really know what you're talking about. The fact that you said the two are "ALWAYS very different" is further proof of that.

The rules of grammar are still being followed as I explained above. You are confusing formal usage with basic grammar. As I said, it's perfectly correct to say "Us old people" in a certain context. Or do PhDs have basic reading comprehension problems?