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.
Bacterial infections on the skin may also cause hair loss, and fungal or yeast infections can lead to excessive shedding. Hyperthyroidism is caused by dysfunctional thyroid gland that will lead to the secretion of too many thyroid hormones. This will result in shedding.