Studying the interplay between the electrochemical performance and the electrolyte conditioning process is crucial for building an efficient magnesium battery. In this work, we use halogen-free electrolyte (HFE) based on Mg(NO3)2 in acetonitrile (ACN) and tetraethylene glycol dimethyl ether (G4) to study the effect of the aging time calendar on its electrochemical properties. The characterization techniques confirm apparent changes occurring in the bulk speciation and the Mg2+ solvation barrier of the aging HFE relative to the as-prepared fresh HFE. The overpotential of Mg plating/stripping and bulk resistance of the aging HFE is reduced relative to the as-prepared fresh HFE. Mg-S cells using aged HFE deliver high specific capacities (586 mA h/g), higher Coulombic efficiencies, and higher cycle life (up to 30 cycles at 25 °C) relative to Mg-S cells with fresh HFE that deliver a specific capacity of ∼535 mA h g-1, low Coulombic efficiency, and short cycle life at a current density of 0.02 mA cm-2. The present findings provide a new concept describing how the aging process regulates the electrochemical performance of the HFE and enhances the cycle life of Mg-S batteries.