TESS Hunt for Young and Maturing Exoplanets (THYME). XIV. A Comoving-based Age Constraint for KELT-20

Abstract Young stellar moving groups offer unique opportunities to investigate the early evolution of stellar and planetary systems. In continuation of an ongoing effort to age-date compelling planetary systems, we provide an in-depth age analysis of KELT-20—a young A-type star that hosts a well-aligned ultrahot Jupiter. This system poses a useful case study to investigate migration mechanisms at early stages of evolution. Using Gaia DR3 data, we identify 77 stars with proper motions consistent with KELT-20, including 19 with measured radial velocities that enable full 3D kinematic confirmation. Using isochronal analyses, gyrochronology, photometric variability, and stellar activity indicators, we converge on an age of 58 ± 5 Myr. This constraint provides critical insights into the dynamical processes shaping hot Jupiter formation.