The increasing incorporation of reclaimed asphalt pavement (RAP) in asphalt mixtures provides substantial economic and environmental benefits but poses challenges due to the stiff and brittle nature of aged RAP binders, which can lead to premature cracking. This study investigates the potential of waste cooking oil (WCO) as a sustainable and low-cost rejuvenator to restore the properties of aged RAP binders. Virgin binders of grade 60/80 and 80/100 were blended with RAP binder and varying percentages of WCO (1–5% by weight). The physical (penetration, softening point, viscosity) and rheological (complex shear modulus G*, phase angle δ, and Glover-Rowe G-R parameter) properties of these blends were evaluated under unaged, Rolling Thin Film Oven (RTFO), and Pressure Aging Vessel (PAV) conditions. Standard tests, including rotational viscosity and dynamic shear rheometer, were conducted to characterize the behavior of the blends. The addition of WCO effectively softened the RAP binder blends by increasing penetration and δ while decreasing softening point, viscosity, and G*. An optimal WCO dosage of 2–3% restored the aged RAP binder properties to levels similar to the virgin binder, balancing improved flexibility with acceptable rutting resistance (G*/sinδ). Short-term aging increased stiffness across all binders, but WCO mitigated viscosity increases. However, long-term aging impacts require further investigation. This study demonstrates WCO’s viability as a rejuvenator for high-RAP asphalt binders, offering potential reductions in mixing and compaction temperatures, improved workability, and enhanced sustainability.