Heart Failure: The most common cause of bilateral pitting edema in the elderly is heart failure, particularly congestive heart failure. This condition leads to fluid buildup in the body, causing edema. The age of the patient and the absence of other symptoms make this a likely diagnosis.

Chronic Kidney Disease (CKD) or Nephrotic Syndrome: These conditions can cause fluid retention and edema due to the kidneys' inability to properly filter waste and excess fluids.
Liver Cirrhosis: Cirrhosis can lead to a decrease in albumin production, causing fluid to leak out of blood vessels and into tissues, resulting in edema.
Deep Vein Thrombosis (DVT): Although less likely without other symptoms, DVT can cause unilateral or bilateral edema if it affects both legs or leads to pulmonary embolism, which might not always present with typical symptoms in the elderly.

Superior Vena Cava Syndrome: A condition where the superior vena cava is compressed or obstructed, leading to edema in the upper body but can sometimes present with lower limb edema if there's significant obstruction affecting venous return.
Lymphoma or Other Malignancies: Certain cancers can cause edema due to obstruction of lymphatic or venous vessels.
Pulmonary Embolism: A large pulmonary embolism can cause increased pressure in the pulmonary arteries, leading to right heart failure and subsequent edema.

Lipedema: A rare condition characterized by the accumulation of fat in the subcutaneous tissue, leading to swelling, typically in the legs.
Myxedema: A condition associated with hypothyroidism, characterized by thickening of the skin and underlying tissues, leading to swelling.
Fabry Disease: A genetic disorder that can cause edema among other symptoms due to the accumulation of a particular type of fat in the body's cells.