This question is impossible for me to answer "accurately".
Okay, I am 44 years old, have a MA in Medieval History, have read mythology, folklore, religion, grimoires, rpgs books, sci fi, fantasty, historical fiction and the like most of my days. I have seen hundreds of movies, listened to thousands of albums. I have seen plays, talked to others on a million different topics, and all the rest.
Is anything left that is truly original? Depends on how you look at it.
I don't run games "out of the box"; I have never had luck with pre-packaged adventures as they never fit the world I have come up with (except for a brief foray in RuneQuest run in Pavis/Big Rubble).
On the other hand, I have come up with characters not exactly like anything I have seen, heard, or read before, come up with new monsters and new treasures. I have scenarios that have elements from five disparate sources and something else beside.
So what percentage is me?
All of it, none of it, 50/50 and something else besides.
I'll leave you to decide and I'll just get back to my games
