This work is based on the development and optimization of a pressurized liquid extraction method to obtain extracts from peanut shells with the highest possible amount/number of bioactive compounds, mainly flavonoids, with senolytic activity and antioxidant capacity. To achieve optimal extraction conditions, a design of experiments approach was employed to perform a limited and relatively reduced number of experiments. The extracts were consecutively analyzed by methods adapted to the peanut shell matrix to determine antioxidant capacity, total flavonoids, and total phenolic compounds. Additionally, a high-performance liquid chromatography coupled with diode array detection method was developed and validated to quantify individual phenolic compounds, with confirmation provided by mass spectrometry. Moreover, amino acid profiling was performed using gas chromatography coupled with mass spectrometry. Finally, the optimized extraction conditions and analytical methods were applied to analyze six commercial peanut shell samples. The results indicate that the optimized pressurized liquid extraction method using ethanol effectively extracts substantial amounts of bioactive compounds, especially flavonoids, which have broad applications across different industries. This contributes to a strategic valorization approach that promotes a Circular Economy.