In this article, a novel energy harvesting (EH) interface for a flexible thin-film piezoelectric generator (FPEG) is proposed for EH from irregular human motion. The traditional thick piezoelectric generator (PEG) based kinetic EH circuits are designed for continuous and sinusoidal inputs from the cantilever-based structures and are not suitable for EH from irregular human motion. The proposed EH interface circuit significantly enhances energy extraction with a load-screening scheme, which minimizes the load capacitance to maximize the PEG output voltage up to 102 V while using the standard voltage 0.18-μm process. An energy-aware wake-up controller is designed to (monitor and) detect the FPEG deformation to assure that the harvesting interface is only activated when enough energy is available for EH. When the FPEG voltage peaks, the energy is transferred to the battery through an inductor with a single-cycle buck-converter-like operation, allowing the input voltage and frequency-independent EH operation. The measurement results show that the proposed EH interface successfully harvests energy from irregular pulsed inputs with 562% improvement compared with a full-bridge rectifier.