What is the likely diagnosis for a well-demarcated, dry, rough, tan-colored area on the forearm of a retired park ranger?

The presentation of a well-demarcated, dry, rough, tan-colored area on the forearm is characteristic of actinic keratosis. This condition arises due to long-term sun exposure, which is particularly relevant for a retired park ranger who would have spent substantial time outdoors. Actinic keratoses typically appear as scaly patches and are considered precursors to skin cancer, specifically squamous cell carcinoma.

A key feature of actinic keratosis is its rough texture, differentiating it from other skin lesions. The tan color and well-defined edges also support the diagnosis. Given the patient's demographic and history of sun exposure, this condition aligns closely with the likely diagnosis.

Keratoacanthoma is usually more dome-shaped and can quickly grow, often resembling squamous cell carcinoma rather than presenting as a dry, rough area. Seborrheic keratosis typically appears raised and has a waxy texture, often waxy and may range in color from light tan to black, differing from the description provided. Senile lentigo, or age spots, is flat and not rough, usually brown and often multiple in nature, distinguishing it from the solitary, rough texture seen in this case.