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.
---Shedding: Common boa constrictors generally have few problems shedding their skin. When a snake incompletely sheds, and a portion of the skin is left adhered to the snake, the snake should be soaked in shallow water or slightly-soapy water for several hours, after which the skin typically comes off very easily.