What is the most likely diagnosis for a 65-year-old male with multiple brown plaques on his back, warty surface, and greasy feel?

The presentation of multiple brown plaques on the back of a 65-year-old male, described as having a warty surface and a greasy feel, is characteristic of seborrheic keratosis. These benign skin lesions are common in older adults and are often seen on the trunk, scalp, and face. They usually appear as well-defined, adherent plaques that can vary in color from light tan to dark brown or black.

The "greasy feel" is particularly indicative, as seborrheic keratoses have a velvety or somewhat oily texture compared to other skin lesions. While other conditions such as lentigines, actinic keratosis, and keratoacanthomas may present with similar colors or appearances, they have distinct features that differentiate them.

For instance, lentigines are flat and uniform in color, primarily related to sun exposure but do not typically have the warty texture associated with seborrheic keratosis. Actinic keratosis usually appears as rough, scaly patches that can feel dry rather than greasy, and they are associated with sun damage and have the potential to progress to squamous cell carcinoma. Keratoacanthomas develop rapidly and may resemble squamous cell carcinomas