What can result from weakening of digestive smooth muscle with age?

Weakening of digestive smooth muscle with age can cause constipation.

Explanation:

Smooth muscles in the digestive system have the role to move food down the tract via radially symmetrical contractions (peristalsis). With age, the function of smooth muscles reduces, causing the food to move more slowly through the alimentary canal (digestive tract). As a consequence, water gets absorbed from food waste, which can cause constipation.