That is false. [1] IQ has an interesting characteristic in that at young age environmental factors play a slightly larger role than genetics in IQ but as the child reaches their late teens their IQ becomes determined primarily by genetics. This is also to say that while a child may outperform against another child at a younger age, due to environmental factors -- if this comparison, even between the same people, was done at a later age then the result would generally be primarily determined by genetics. In other words the gains (or deficits) experienced in childhood do not carry on to adulthood - as counter intuitive as that may be.
> "IQ testing was invented by a certain demographic and as you would expect works best on people that take the test which fall under that demographic."
Comparing the IQ of nations is extremely difficult and plagued by a number of possible confounding variables. So that has to be taken into consideration, but nonetheless the majority of data that is available contradicts what you're saying. IQ testing was developed in Europe/England. It tends to be Asian nations that score the highest on IQ exams. I'm not linking to any particular source here since so far as I know this is completely fundamental - any source would verify as much including the one in the post I'm responding to.