Oddly enough, in the 1970s, it started to be used, and accepted, to describe not just groups of males, but groups of males and females. I have even heard it used to describe groups of females. It's still being used this way now, and apparently has to be preceded by the word *you*. Of course the word *guy* has never changed, it means a young man. So, you can confidently address a group that has both males and females as *guys*. But only a male in that group can be called a *guy*. A female can never be called a *guy*.
My ancestors have been speaking English for thousands of years. But that doesn't mean that I always know what they were talking about!