I like the concept of fluid and crystallized intelligence. The one aspect decreases when you grow older, the other increases. The Cattell-Horn theory of fluid and crystallized intelligence suggests that fluid intelligence is the ability to reason and think flexibly. Crystallized intelligence refers to the accumulation of knowledge, facts, and skills that are acquired throughout life. So one's IQ would be a combination of the two.
People often claim that their intelligence seems to decline as they age. However, research suggests that while fluid intelligence begins to decrease after adolescence, crystallized intelligence continues to increase throughout adulthood.
https://www.verywellmind.com/fluid-intelligence-vs-crystallized-intelligence-2795004