Achalasia: A motility disorder of the esophagus characterized by the failure of the lower esophageal sphincter to relax, leading to progressive dysphagia. The subacute progression and age of the patient make this a plausible diagnosis, although it's more commonly diagnosed at a younger age.

Esophageal Cancer: Given the age and progressive nature of the dysphagia, esophageal cancer is a significant consideration. It can cause mechanical obstruction leading to dysphagia.
Benign Esophageal Stricture: This could be due to chronic gastroesophageal reflux disease (GERD) or other causes like esophagitis, leading to narrowing of the esophagus and difficulty swallowing.
Esophageal Spasm or Diffuse Esophageal Spasm: Although less common, these motility disorders can cause dysphagia, especially if the spasms are severe and frequent.

Esophageal Perforation: Although less likely to present with subacute progressive dysphagia, any condition that leads to a perforation (e.g., iatrogenic from an endoscopy, foreign body, or severe esophagitis) is an emergency and must be ruled out promptly.
Mediastinal Mass: A mass in the mediastinum can compress the esophagus, leading to dysphagia. This could be due to lymphoma, metastatic cancer, or other mediastinal tumors.

Eosinophilic Esophagitis: An inflammatory condition of the esophagus that can cause dysphagia and food impaction, more commonly seen in younger patients but can occur at any age.
Scleroderma: A systemic disease that can affect the esophagus, leading to dysmotility and dysphagia. However, it usually presents with other systemic symptoms.
Chagas Disease: Caused by Trypanosoma cruzi, leading to achalasia-like symptoms due to destruction of the myenteric plexus of the esophagus. It's rare in the United States but should be considered in patients from endemic areas.
Amyloidosis: A condition where amyloid proteins deposit in various tissues, including the esophagus, potentially leading to dysphagia. However, this is a rare cause of esophageal symptoms.