That begs the question then, what happens to these early-20s geniuses once they are late 20s/30s?
I’ve had that surreal “we really want you to stay but we can’t give you a raise” conversation too many times in my career.
Then a subset of the gifted technical individuals grow tired of management, step down and go back to the tech to do what they really loved all along.
I've met a fair amount of brilliant engineers in their 40s/50s who have been through management and decided it's not for them and are now shining as engineers again after a decade lost to leadership roles
To answer your question, they get swallowed. Google etc hoard talent, and those that can fake it. I don't know if that's good, but they definitely end up with resources to produce incredible things. Then again what would they do alone, I wonder.
Learning is the key to flying high when it comes to a knowledge intensive career like programming.
Its hard to do that a while. Also early 20's you just exit teenage, and a have degree of naivety and foolishness. That spark goes with time. And you become more intelligent, calculative and serious to stop experimenting the way you are before.
But mostly, they stop learning. That's what causes the downfall.