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.
To leave their old skin behind, snakes may go for a swim to allow water to loosen the old skin even further. When they're ready to shed the old layer, they create a rip in the old skin, usually in the mouth or nose area. They often do this by rubbing against a rough, hard object, such as a rock or a log.