First, it is obvious that, in the top, a young smart person will beat an older one in the kind of tests that IQ tests measure. You can see that in sports either, speed beyond strength is one obvious one.
In average, young education could play a big role and better education in the old could beat a worse education. For example, an average observation, my father on his late 70s beats people in their 20s in doing mental math not because he is a genius because his generation had a better general education in math than the people at 20s. My dad is far from being a genius, he is not dumb either! but his average skills, as measured by IQ are obviously higher than the average young. Clearly my dad is now slower but also on language skills is fast enough to beat in associations an average young.
Now, we are in 2024 and we need to reassess what IQ measures in terms of intelligence pragmatism. Also, the smart individual vs the smart group. For achieve success, even in the research laboratory you should forget about individual IQs and think differently.
Another corollary for this is that psychology, at some extent, is time dependant and the trues from the 1900s could be falsenin 2024. It is not like math.