Degradation mechanisms accelerated by harsh conditions (high temperature, electrical stress) can affect circuit performances. Submitted to electromagnetic interferences, aged components can become more susceptible, which stirs up questions about the safety level of the final application. Unfortunately, the impact of circuit aging on its susceptibility level remains under evaluated and is not taken into account at circuit design level. This paper presents a first attempt of a modeling methodology aiming at predicting the impact of circuit aging on the susceptibility to electromagnetic interferences. This methodology is applied to model and explain the measured variations of the susceptibility level of phase-locked loop after an accelerated-life test.