While I regard psychometrics as utterly useless in some of it’s applications, there is some empirical support for general intelligence, (g factor). While fluid intelligence is assumed to be responsible for ‘general intelligence,’ such as learning, critical thinking, analysis and pattern-recognition, crystalized intelligence is assumed to be responsible for the allocation, recollection and application of acquired knowledge, associations, perceptions and experiences. I know that some researchers posit a peak in fluid intelligence during early-to-middle adulthood and a gradual decline shortly after. Crystalized intelligence is assumed to remain relatively stable over one’s adult life and only begins to gradually decrease around the age of 60.
While there is some strong correlation between aspects of the physical structure of the brain and general intelligence, the problem is still very open. It is postulated (through the extrapolation of data from research), that fluid intelligence involves the dorsolateral prefrontal cortex, the anterior cingulate cortex and other systems related to short-term memory and attention. Crystallized intelligence is assumed to have a strong correlation with brain regions that involve the storage and usage of long-term memories, such as the hippocampus. However, there is no general consensus amont cognitivsts or neuroscientists, regarding intelligence. In fact, there is no consensus on what intelligence is (for instance, a tribe in the amazon would not value 'mathematical intelligence' and an ability to do riemannian geometry in your head but would value quite highly, an intelligence associated with survival or harvesting of food). Without a general consensus regarding intelligence, it is hard to discover the causal pathways between electrobiochemical reactions/physical structure and intelligence. I do believe that the g factor has strong empirical support, it is only through specific presupposed axioms or postulates about intelligence, that it can be derived. Without strong empirical support for physical causal relationships with intelligence or even some concenus on what intelligence is, I remain skeptical.
Tests can derive heritability between specific aspects of general intelligence and physical structures of the brain, (of which there is documented research for) as well as a correlation between g factor and rats. While there is a positive correlation between g factor and academic/career performance, the causal pathways are largely unknown. Research supporting strong correlates includes, overall brain mass, glucose metabolization rate within the brain, and the mass of the prefrontal lobe. There is conflicting evidence regarding the correlation between g and peripheral nerve conduction velocity (which is calculated by measuring the distance between electrodes and the time it takes for electrical impulses to travel between electrodes), with some reports of significant positive correlations, and others of no or even negative correlations. The fact that there is conflicting data and research is not a surprise (it is a necessary aspect of research), however, it does suggest a lack of unification between the g factor and intelligence (or perhaps the consensus among researchers).
While I am certain and aware that documented cases exist regarding a correlation between a decrease in academic/career performance and the g factor, I still feel as though it is largely inconclusive.
I would approach psychometrics with a weary perspective and be certain that you have looked through some of the research pertaining to it. If you read through the research and determine that you still embrace psychometric testing, than all is well. I, however, I yet to be convinced.
So my answer is that, no, I do not think I can conclusively support your hypothesis.