On his Wikipedia page, in the 1966 - 1975 section it says it took a lot of persuasion to get him to use the wheelchair. This suggests that he wasn't in dire need of it at that point. His first child was in 1967, the last in 1979.
6. Extremely high ammonia levels in the water can damage the outer layer of skin and cause shedding. RES are tolerant of high ammonia levels while map turtles are not, so this problem is more likely to occur with Graptemys species.
Unlike other animals, snakes continue to grow until the day they die. Consequently, snakes periodically shed their skin in a process called ecdysis.. Before shedding the skin, the snake takes on a slightly bluish hue and the eyes appear cloudy. This is caused by fluid located between the layers of skin. Mites, malnutrition, and trauma, among other things, may cause dysecdysis, or abnormal shedding. The skin is normally shed all in one piece, including the brille.