Cattleman's Steakhouse, located centrally in OKC, has been serving aged beef since 1910. It is a small restaurant located about four-blocks south of I-40 in what is known as "Stockyard City"—a place for farmers and cattlemen to buy supplies, apparel, food, etc.
The food is good, the service is great, and the restaurant has a relaxed and fun ambiance. Recommended more for the experience than the food.