Lipoma: A benign tumor composed of fat tissue, which is common in older adults and can present as a hard, painless lump. The location near the clavicle is plausible for a lipoma.

Cyst or Abscess: Though less common in this specific location without signs of infection, a cyst or abscess could present as a hard lump, especially if it becomes chronic or encapsulated.
Enlarged Lymph Node: Given the proximity to the clavicle, an enlarged lymph node could be considered, especially if there's an underlying infection or inflammation, even if not immediately apparent.
Benign Bone Tumor (e.g., Osteochondroma): These can occur near the clavicle and present as a hard, painless lump, though they are less common.

Metastatic Disease: Although less likely without systemic symptoms like weight loss, metastasis to the clavicle or adjacent lymph nodes from a primary cancer (e.g., breast, lung, or thyroid) could present as a hard lump and is critical not to miss due to its implications for prognosis and treatment.
Primary Bone Malignancy (e.g., Chondrosarcoma, Osteosarcoma): These are rare but would have significant implications for treatment and prognosis, making them crucial not to overlook.

Paget's Disease of Bone: A condition that can cause an abnormal breakdown and regrowth of bone tissue, leading to deformity. It's rare and usually presents with bone pain, but a lump could be a presenting feature in some cases.
Ewing's Sarcoma: A rare type of cancer that typically occurs in bones or in the soft tissue around the bones, more common in younger individuals but could be considered in a differential diagnosis due to its aggressive nature and potential for rapid growth.