Although intellectual engagement is a significant factor associated with adult cognitive health, it is unclear what it includes, why and how it declines across the lifespan, and importantly, whether its decline has a causal role in cognitive aging. This integrative review introduces a novel theoretical life course framework that synthesizes research on early childhood experiences and cognitive aging to address the following three points. First, we specify six critical factors of intellectual engagement for long-term, broad cognitive development: (a) open-minded input-driven learning, (b) individualized scaffolding, (c) growth mindset, (d) forgiving environment, (e) serious commitment to learning, and (f) learning multiple skills simultaneously. We show that these factors increase basic cognitive abilities (e.g., working memory, inhibition) and promote far transfer. Second, we trace the decline of the six factors from infancy to aging adulthood (broad learning to specialization). Finally, we propose that these six factors can be applied to expand cognitive functioning in aging adults beyond currently known limits.