Gravity. What an effect it can have on aging skin. Unfortunately, a sagging jawline is no exception. Your jaw is one of the three areas gravity is constantly working against. Not to mention, our skin has already betrayed us by age 20 when it starts to thin. By the time we hit 40, we can start seeing wrinkles and sagging skin in the lower face. Around 50, we start losing bone, fat and muscle in the jaw area.