Ultrafast laser surface structuring is a promising approach for controlling surface functionalities like surface wettability. Extensive studies have been devoted to this area, and researchers have successfully achieved a spectrum of surface wettability ranging from superhydrophilicity to superhydrophobicity across various materials. However, long-term storage in ambient air exposes a stability challenge for ultrafast laser-induced surface wettability. The surface wettability could turn from superhydrophilicity to superhydrophobicity over long-term storage. It is critical to understand the mechanism of the aging mechanisms and its impact on wettability change. This study investigates the effect of aging on stainless steel after femtosecond laser surface structuring. The static contact angle is used as the measurement of surface wettability. The effect of different storing environments, types of surface structures, and surface roughness are studied. Surface morphology is characterized using scanning electron microscopy, and surface chemistry is measured through X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy. Hypotheses for the aging mechanisms are proposed and testified. For the first time, it is demonstrated that although the aging effect is caused by the surface chemistry change, surface morphology and roughness could have a direct impact on the process. A semi-quantitative equation is developed to describe the aging process and agrees well with the experimental observation. This marks a significant step forward, providing insights into the intricate interplay between surface characteristics and aging dynamics.