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.
As the bones of the turtle grows, the scutes do not (for most species of turtles). As the turtle grows, new (larger) scutes are growing with it. The top (smaller) layer of scutes will loosen and peel off. Scute shedding is a totally natural process.