I don't get why there would be uncertainty to begin with? Credence is stated to be early 20s in the script and that's also the age of his actor. He hardly looks like a teenager. How is that uncertain at all? Because the film doesn't explicitly say his age? They don't state Newt or Queenie's age either, but fandom takes for true the age we're given in the supplementary materials. Why is Credence different?
I don't mean to be rude, but I've seen far too much #discourse about how shipling Credence with anyone is dirtybadwrong and I'm tired of it. We have a couple different sources saying he's over 21. Unless the fic author or prompter deliberatelt want to change his age, he's not a minor.