Gynecomastia: This is the most common cause of breast lumps in men, especially in the older age group. It is characterized by the benign proliferation of glandular tissue in the male breast, often due to hormonal imbalance. The patient's age and the location of the lump below the nipple are consistent with gynecomastia.

Lipoma: A benign tumor composed of fat tissue, which can occur in the breast area and cause a palpable lump. Lipomas are common in older adults and can cause slight discomfort.
Breast Cyst: Although more common in women, breast cysts can occur in men. They are fluid-filled sacs that can cause lumps and may be tender to the touch.
Fibroadenoma: A benign tumor of the breast tissue, which can occur in men, though it is less common than in women. It typically presents as a firm, movable lump.

Breast Cancer: Although rare in men, breast cancer is a critical diagnosis not to miss. It can present as a lump, and while the incidence is lower in men than in women, it is often diagnosed at a later stage due to lack of awareness and screening.
Infection or Abscess: An infection of the breast tissue can cause a lump, soreness, and discomfort. It is essential to consider this diagnosis, especially if there are signs of inflammation or systemic infection.

Phyllodes Tumor: A rare tumor of the breast that can be benign, borderline, or malignant. It tends to grow quickly and can cause a large lump.
Sarcoidosis of the Breast: Sarcoidosis is a condition that can affect various parts of the body, including the breast, causing lumps and inflammation. It is rare and would be an unusual cause of a breast lump in a male patient.
Metastasis to the Breast: Rarely, cancers from other parts of the body can metastasize to the breast, causing a lump. This would be an unusual presentation but is a consideration in patients with a known history of cancer.