I wonder how many of these folks were "big thinkers" just without the proper stimulus? Or in other words, did most of them come up with various other ideas throughout their life -- perhaps in various fields -- and it finally just worked out where all the pieces were in place at the right time? Or did these people undergo a personality change in their middle years? I suspect the former. Midgley's and Kroc's stories especially sound like people who were "accumulating" and working out ideas for many, many years before it finally gelled, but it's just a guess.
When the 22-year-old hits it big with some idea we all say something like "Look at that awesome kid! He was born for greatness" but when a 44-year-old does the same thing, we can no longer use the "he's so special it's no wonder he succeeded" rationale. Something else is at work.