Which of the following best describes the decline of fluid intelligence?

The decline of fluid intelligence refers to the cognitive abilities related to reasoning, problem-solving, and the capacity to adapt to new situations. This type of intelligence is influenced by the brain's processing speed and the ability to work with abstract concepts.

The choice stating that fluid intelligence begins to decline gradually in middle age accurately reflects research findings. Studies show that while some cognitive abilities remain stable throughout adulthood, fluid intelligence tends to peak in early adulthood and then experiences a gradual decline as individuals enter middle age. This decline is not abrupt but rather a gradual process that can vary widely among individuals.

The other choices do not align with the established understanding of fluid intelligence. For instance, stating that it occurs rapidly after adolescence would contradict the evidence indicating a slower decline starting in middle age. Asserting that it is not affected by age ignores the research that has documented changes in cognitive abilities over the lifespan. Lastly, suggesting that fluid intelligence increases consistently with age misrepresents the typical trajectory observed in cognitive aging.