From Nearly Roadkill by Caitlin Sullivan and Kate Bornstein, first published in 1996.

I had no idea how old ze/hir pronouns were, but clearly they’re at least 20 years old.  

How many decades does something have to be around before people consider it valid?

In August 1920, the Sacramento Bee newspaper proposed its use.

All writers and most readers, in fact, have felt the need for some single pronoun which would take the place of the words “he or she.” The Bee accordingly coins the word “hir” to do this service…In these days of superabundant verbiage, such short-cuts to brevity and clearness can logically be taken, should be. Therefore, “hir.”

Source Steve Wiegand, Papers of Permanence: The First 150 Years of The McClatchy Company

The word has literally been around for almost 95 years. Even by conservative language standards, it’s pretty much a word. Even if it was just coined yesterday, I would still support hir as a word.

And when it comes to ze, it’s a pronoun that was basically derived from the german pronoun sie back in 1972.

ze (from Ger. sie), zim, zees, zeeself; per (from person), pers Steven Polgar of Chapel Hill, North Carolina, proposes the ze paradigm; John Clark offers per. Newsletter of the American Anthropological Association 13 (September): 17-1 [1]

So it’s been around for over forty years. As with the other pronoun, even if it was extremely new, I’d still defend it. Language is alive and breathing and evolves to serves communities and to deny these pronouns being “real” words means you’re a cissexist shit.