The use of the word 'guys' near the end

The word guy as an American slang term for a male goes back to the 1840s, and its collective usage to address a group came not long after, albeit it was mostly heard in large cities in the East. By the 1920's it was used frequently as a casual form of address and would have been interchangeable with terms like fellas and folks (though folks would have had a more rural, wholesome connotation in its usage and would probably not be often used by city-types unless they were trying to evoke a specific feeling in their language).

The most immediate proof I can think of is the film Guys and Dolls. Even though that's from the 50s, it at least shows that the term "guys" didn't crop up in only the last 15 years. Some stuff has been around long before the 21st century. ;)

You did not address or refer to a group of woman as guys until the 1970s as far as I know. A girl calls a group of girls "guys" in Animal House, which is the first time I noticed it used that way. But the word guy was common in referring to men a long time ago. "Guy" means "man."

Yeah, to clarify - my point was that addressing a group of mixed gender people as guys is a fairly recent thing.

I definitely remember "guys" being used to address mixed male/female groups, and even groups of girls, as far back as the early 1960s, and I doubt that it was new then.