As a Clinical Psychologist, I ask, have they really done any longitudinal research by reading the literature and performing any experiments concerning this problem? Obviously not. Professional literature is replete with articles concerning this topic. IQ can change over time but few people realise that IQ tests provide the same answer, i.e. scores, etc., to a great extent, even over a period of one year. The older a person is the more the test scores remain the same. It has been shown that children can have increased volatility in IQ scores is in childhood but it occurs mostly in adolescence but much depends on the environment in which they were raised.
Could go on but the pundits know better than to listen to read or such details as it may cause them to develop headaches, etc.