It went something like, the reason there are only child prodigy, and no adult prodigy, is because other kids eventually catch up. And that child prodigies are basically just children that are ahead compared to other kids of the same age.
It looked at the data, and showed that once adult, child prodigies just distribute themselves similarly accross all levels of accomplishments, success and failures as any other adult.
It also said that, once adult, the difference between the best, second best, third best, and all following is much less pronounced, and therefore no one looks so far superior to anyone else who had similar training, opportunity, luck, etc.
Whereas with children, the difference is stark, so people take notice, and that's where the "prodigy" is born.
I can't remember the source, so take it all with a grain of salt, but I always thought it was an interesting article, and a good question, where are all the adult prodigies?
Edit: Also, I vaguely remember it saying that the data shows a higher level of depression and general less happiness in now adult child prodigees, which the article hypothesized might be either from the loss of "being special", or from the weird childhood that "being special" created.
My only plan is to share with family members and ensure records don't get lost.