Research on aging has advanced rapidly since the early 2000s, evolving from studies at the cellular level to investigations of aging in whole organisms. Beginning with research on telomerase, recent advances in controlling the expression of the Yamanaka factors have raised the possibility of reversing aspects of biological aging. In parallel, a wide range of rejuvenation strategies—including the elimination of senescent cells, young blood–based therapies, and cellular reprogramming—are being actively explored. However, it remains uncertain whether rejuvenation observed in specific cells or tissues can be translated into meaningful rejuvenation of the entire organism. There are also concerns that reversing aging may promote abnormal cell proliferation and increase the risk of diseases such as cancer. Despite these challenges, rejuvenation research represents one of the most promising approaches to addressing population aging and extending healthy lifespan. Can we truly reverse the aging process?