<p>As the earliest aging organ in females, the ovary undergoes functional decline and structural senescence that drive reproductive system alterations. Central to this process is the primordial follicle—the non-renewable reserve of female germ cells and the sole source for oocyte development. The primordial follicle pool is established prenatally, fixed in quantity, and cannot regenerate after birth, serving as the fundamental biological reserve that determines both fertility potential and reproductive lifespan. Once depletion begins, it is irreversible, directly limiting the reproductive window and influencing ovarian endocrine function. Therefore, this review briefly summarizes the latest research progress on primordial follicle development, providing an in-depth analysis of primordial follicle dormancy and activation mechanisms as well as therapeutic approaches for associated complications. This work holds significant implications for understanding reproductive aging, preventing and treating reproductive endocrine disorders, and developing novel fertility strategies, offering valuable references for comprehending the biological mechanisms and potential applications of primordial follicles.</p>