What is the treatment of a single leg ulcer in an much older man?

Depends: Leg ulcer can be a tip of the iceberg. The causes are many so the treatment varies greatly. In the elderly population, vascular disease (artery, vein, and lymphatics), infection, accident/pressure induced soft tissue injury, metabolic issues including diabetes makes healing difficult. Do not delay medical attention, some ulcer can get aggressive and cause big problem.

Ulcer: It depends on the cause In general the most important thing is to elevate the leg to reduce swelling which helps in the healing process