Is the droopy lower eyelid on the same side as the limp? what is causing the limp? A wound in the pad of the foot? A nail, a stone in between the toes? Canine arthritis?
Many old dogs have droopy eyelids. Muscle fatigue may bring on droopy eyelids.
Check the diet of the dog. What is the dog eating? Dogs that are fed only cereal based dog food may not be getting enough collagen (from tendons, meats, animal fat) and the skin literally loses elasticity.