People who design IQ tests keep making them increasingly tougher to master due to the Flynn effect.
The subjective effect of this policy on the population over time is that your tested IQ* will usually keep falling after you reach optimal brain function (circa 22), the shrinking number flying in the face of everything we know regarding experience & long-term cogitation as enhancers of intelligence. Also note that we know that at least in children, the social self-image developed in school - brainy nerd or dumb jock - has a real corresponding effect on their subsequent development of intelligence. IQ isn't just controversial - for a growing elderly demographic it may be becoming literally toxic.
Average IQ is a value with no net numerical accuracy over time.
This contradiction appears insoluble.
* Mine was 187 as a wee sprog circa 1972, burned down to thirty points less by the last test I took, circa 2000. Makes for a jocular little thought-experiment to work out that long before my 500th birthday, my IQ would inevitably reach zero.