These people do exist, though. Just like in any sufficently deep intellectual field, there are people who are very gifted and have insane focus. Compounded over years, they grow to be real beasts, just listen to any talk by John Carmack or Jonathan Blow. The bad news for the employees is that they tend to start their own companies, as typical firms don't have appropriate spots for them (as someone else mentioned, these people provide 10x value but are typically only paid 1.5x-2x).
Sure, a games company or similar, but would Carmack be a 'rockstar' on something like a node.js stack? I'm sure he could pick the tech up quickly, but most of his skills lie elsewhere. And yet there is the expectation in tech that truly experienced people will be good at everything, just look at the post about 'things I don't know' from yesterday to see examples of this expectation.
But also, they tend to be less of talkers and presenters which is another separate skill. As in, they are rarely public face.
2.) If you are hiring for vague sense that person grows in 10 years, you are extremely likely to be biased for all kind if cultural and demographic signals that have zero with actual performance.
3.) Old are not wizards now, for dame reason why young are not wizards now. Nobody can know everything and wizardly is moving target - half composed of myths and half of smokescreen.
It is not to say that great people don't exist, they absolutely do. But they all have expertise in what they do now and when they change jobs, there is learning curve.