What is the locality that you found the turtle? This would help. My guess is that it is a large male of one of the Eastern Box ssp. Often older individuals will have muted markings, that may come in the form of different shades of brown/tan. Some extra large males also exhibit a more elongated appearance. Also, Wood Turtles do not have a hinge on their plastron. Let us know a little more info, and we will help you zero in on the exact species.