The purpose of this FOA is to invite both descriptive studies to identify putative juvenile protective factors, experimental studies to test hypotheses about their effects on aging, and translational studies to explore the potential risks and benefits of maintaining or modulating the level of juvenile protective factors in adult life. Juvenile protective factors are physiological factors that maintain or enhance certain functions across all or some stages of post-natal maturation, but which diminish or disappear during transitions between developmental stages (e.g., infancy, adiposity rebound, adrenarche, puberty, growth cessation). This FOA is uniquely focused on studies which involve comparisons between post-natal developmental stages or pre- vs. post-maturational changes to identify potential juvenile protective factors and their effects on aging. Studies in in vitro models, in laboratory animals or in humans may be proposed.