As the use of reclaimed asphalt pavement (RAP) in asphalt concrete mixtures increases, it is important to understand how the addition of asphalt binder that has already been aged affects the overall properties and performance of the mixture. In this study, four plant-produced mixtures containing 0%, 20%, 30%, and 40% RAP were aged long-term in an oven in the laboratory to three levels. The dynamic modulus was measured for each aging level and compared with unaged values to determine whether there was a statistical difference. It was found that as RAP content increased, aging had less effect on stiffness; this finding was quantified with areas under the dynamic modulus curves and aging ratios. The greatest differences were observed at the high-temperature and low-frequency ranges. The study also showed that the slope of relaxation modulus was less affected by aging as RAP content increased. The Global Aging System (GAS) was used to predict the change in dynamic modulus over time with the virgin binder properties. This method overpredicted the measured changes in stiffness. The GAS was also used to predict how many months of service life were simulated for each mix by long-term oven aging. It was found that as RAP content increased, hot-mix asphalt mixes stiffened at a slower rate than virgin mixes.