This is not a new discovery. It's known as the Flynn effect. [1] It initially was the observation that IQ scores were constantly increasing over time. This was one of big correlations in support of intelligence being driven by environment. Our environmental conditions were improving, and so was our IQ.

But then sometime starting around the mid 90s it began to reverse in developed nations. And by reverse, I mean IQ's began declining - not approaching some sort of asymptotic 0 level of growth. So, if we normalize for age, an average person born in the 70s will have a higher IQ than an average person born in the 90s.

[1] - https://en.wikipedia.org/wiki/Flynn_effect