I hate when people praise me for being "intelligent" because I posted a link to one of my code projects. I think it's not intelligence; it's skill¹.
Intelligence isn't a quantifiable medium because intelligence depends on various other factors: skill, memory, pattern recognition and maturity just to name a few.
If you've met me in a physical form, and become one of my close friends, you will probably know I'm the opposite of mature; considering I shout random shit into the skies.
Since, as of right now, we don't have a list of the factors that affect intelligence to my knowledge, we can't just put a test in front of someone and instantly know their intelligence.
School exams measure memory, work ethic and ability to apply information; not intelligence. Ironically, IQ (intelligence quotient) tests don't measure intelligence; they measure pattern recognition and memory.
Even if we could test intelligence, how could we possibly put it into numbers? Percentage would not be usable because who would be defined as the 100%? What if someone was over 100%?
Numbers can be ambiguous, is 1 good or bad? 0.500; is it half of 1 or halfway to the best?
The fundamental problem of ambiguity and all the different factors shows us that intelligence is indeed unquantifiable².
 If you think I'm flexing on you because I can write software, you're wrong; read on past the first paragraph.
 Did you think I was more intelligent for using semicolons and fancy words? Vocabulary is a factor of intelligence too!