Under-eye bags during aging result from a combination of factors including the weakening of muscles, loss of skin elasticity, accumulation of fat, and fluid retention, leading to puffiness and swelling beneath the eyes. The muscles and tissues that support the lower eyelids can weaken over time, leading to a gradual sagging of the skin beneath the eyes. As you age, the skin becomes less elastic due to a decrease in collagen and elastin production. This can contribute to the thinning and loosening of the skin, making under-eye bags more prominent.