Abstract Numerous efforts in wireless power transfer have concentrated on simultaneous wireless information and power transfer (SWIPT), enabling terminal devices (TDs) to achieve permanent operation and reducing the limitation of energy on information transmission. Nevertheless, most existing studies focus on the amount of energy transferred, the estimation of the harvest states of TDs, and the optimization of energy efficiency for a system, failing to investigate the timeliness of energy replenishment for TDs through wireless energy harvesting. Additionally, due to channel fading and the influence of nonlinear circuits, serious estimation errors will occur during wireless energy transmission and state of charge (SoC) evaluation, resulting in the failure of system strategies and degraded system performance. To address this issue, a novel wireless energy access quality of service (QoS) index, age of energy harvesting (AoEH), is proposed to measure the timeliness of wireless energy transfer for TDs. Based on AoEH, this paper establishes a SWIPT access channel model and revises the time sequence of access channels. Furthermore, an energy management strategy is proposed for the permanent operation of TDs, and relevant theoretical analysis on the boundlessness of remaining energy is provided. As a typical case, this paper formulates the age of information (AoI) minimization problem for SWIPT-enabled sensor networks to find the optimal energy packet generation interval at the sink node based on AoEH expressions. Corresponding solutions are proposed for the AoI minimization problem with and without maximum transmission frequency constraints. Simulation results indicate that TD’s energy is bounded and stable under the proposed energy management strategy, and the AoI optimized by the optimal energy packet generation interval algorithm is up to 30% lower compared to existing algorithms.