Similar to the plague of mental health, people often point to an individual's (their own or another's) "Intelligence Quotient" as some kind of credential. Of course, such a credential is nonsense for all of the normal reasons citation-dependent arguments often are, but also a host more.
The biggest problem is that any intelligence test would be superstituous nonsense because it's impossible to neutrally define who's more "intelligent". The only way to establish scientifically that your test is accurate is to show that people who score higher on it are smarter outside of it. Therefore it begs the question. You have to already agree on who's smarter for a wide range of test cases to establish the validity of this test. And of course such a thing is entirely impossible. Let alone the thought of reducing "intelligence" to a single number, that's just laughable.
But it's wrong for even more reasons. Such a general credential is incredibly dangerous.
Normal credentials - like having a degree in biology for example - are meaningful because that's a factual domain and not an inherent part of being human. It's also well-defined; it's clear what that credential is useful for. It allows you to make qualified claims about biology and have people take your word for it, provided your honesty isn't in question. That's the point of a credential.
But when someone's credential is "I have an IQ of 150", what is that even useful for? Does that mean every time they disagree with you they can just say "I'm smarter than you so you should take my word for it"? There are no limits on what that encompasses. It can't mean anything without meaning everything. It fundamentally threatens freedom of thought by giving people all-encompassing authority.
Also the age scaling. It's hard to find clear information on the internet but from what I've read the final "IQ" score is your raw score divided by your age... with adults counted as 18. Otherwise adults would be judged to be stupid and the inherent stupidity of age scaling would be exposed. Really, are you going to pick that arbitrary number to cap it at based on the "fact" that people you've sampled stop getting smarter at 18? Now you're just reverse-validating whatever intelligence curve exists: if the reason people stop getting smarter at 18 is because of a problem with the way our education works, you're making damn sure we'll never find out about it by sweeping the evidence for it under the rug.