Well ... some progidies are admired just because they are young and "cute", not because they perform in any way better than the average, middle-aged, professional pianist. So, when they are adults, they are just average too.
We tend to seek for patterns all the time. For trends. If an eight-year-old plays like an adult, we tend to go "ooh, just IMAGINE how good she will be in twenty years!" because we see the development curve keep on skyrocketing. But it might very well be that she is already near her peak and then not much more will happen.
Why are we always favorizing the fast starters? Just imagine some nobody who starts to play the piano in his teens, makes a very modest progress in the beginning but diligently keep on developing until he at the age of 45 is REALLY good - isn't that also a person to admire? We don't call that person a "talent". In fact, we sometimes even mock the poor fellow because he is such a slow starter ... therefore we assume he is "bad"!
Well, we all have our own path to follow. I think our whole traditional school system is crazy, by the way. The idea of putting everyone, born in the same year, in the same group and then just assume they will develop in the same pace during the forthcoming 10 years - how crazy is that? And so we call the fast starters "talents" and the slow starters "failures" ... What an effective (and totally contraproductive) way of making the majority of the population feel like they are no good!
So, I'm not a fan of comptetitions in the music world, especially not for young musicians. They may be fun and encouraging for the partipants, but they can also be the opposite, and they are certainly not "everything".