In recent decades, polymers of intrinsic microporosity (PIMs), especially the firstly introduced PIM-1, have been actively explored for various membrane-based separation purposes and widely recognized as the next generation membrane materials of choice for gas separation due to their ultra-permeable characteristics. Unfortunately, the polymers suffer substantially the negative impacts of physical aging, a phenomenon that is primarily noticeable in high free volume polymers. The phenomenon occurs at the molecular level, which leads to changes in the physical properties, and consequently the separation performance and membrane durability. This review discusses the strategies that have been employed to manage the physical aging issue, with a focus on the approach of blending with nanomaterials to give mixed matrix membranes. A detailed discussion is provided on the types of materials used, their inherent properties, the effects on gas separation performance, and their benefits in the suppression of the aging problem.