<p>The dentate gyrus is a critical hub for hippocampal-dependent memory and is distinguished by its capacity for lifelong neurogenesis, resulting in a heterogeneous population of granule cells generated across embryonic, postnatal, adolescent, and adult stages. Although extensive work has examined the functional contributions of immature adult-born granule cells, whether granule cells born at different life stages retain distinct functional roles once they reach maturity has remained largely unexplored. In this review, we synthesize findings from anatomical, physiological, and behavioral studies that, while not designed to address this question directly, collectively support the proposal that temporal origin constitutes a previously underappreciated organizing principle of dentate gyrus function. We argue that neurons born at different life stages differ not only in their morphological and electrophysiological properties but in the distinct aspects of memory functions they support. Understanding how neuronal birth timing shapes hippocampal computation across the lifespan may have broader implications for conditions in which memory is compromised, from cognitive aging to neuropsychiatric and neurodegenerative disorders, and we hope this framework encourages the more systematic, temporally precise investigations that will be needed to explore them.</p>