Why are my feet and ankles swelling?

Edema. Many things can cause swelling of your feet and ankles. Local factors such as venous insufficiency or varicose veins, or phlebitis or blood clots of the veins can cause this. Liver disease, heart disease and kidney disease can also cause swelling. Malnutrition with low blood protein levels can cause this. If it persists you should be examined and have blood work.
88 Years Old. Swelling of the ankle and feet is relatively frequent symptom in most people. In itself it does not represent a disease but rather the symptom of an underlying disease such as heart disease, liver disease, kidney disease (all of these diseases can influence fluid mobilization in the body by physical, metabolic and electrolyte-water interactions). It would be best to consult your doctor.
In an 88 year old. there can be many reasons including venous insufficiency, side effect of medication, heart and kidney issues should be considered. Best to be evaluated by your PCP.