This paper discusses how growth and aging became interrelated phenomena with the creation of gerontology in the United States. I first show that the relation of growth to senescence, which had hardly attracted scientific attention before the twentieth century, started to be investigated by several experimental scientists around the 1900s. Subsequently, research on the connection between the two phenomena entered a new domain through the birth of gerontology as a scientific field comprised of various disciplines, many of which addressed growth. Due to gerontologists’ efforts, the association between aging and growth became stronger and more multifaceted within the discursive and organizational matrix constituting the new science, leading to a broader definition of senescence with an ambiguous connection to chronological age. Furthermore, as gerontologists borrowed the cultural agendas as well as research methods from studies of growth, aging began to be defined as a phenomenon that could be actively controlled and managed in both social arenas and laboratory environments.