So you are saying that for example the first time generation X takes an IQ test at 15 and gets a 100 score on average but now my son generations takes the same

So you are saying that for example the first time generation X takes an IQ test at 15 and gets a 100 score on average but now my son generations takes the same test at 15 and gets 10 points lower, its probably because gen X had been "training" to take IQ tests?