this is a good point. Similar to minimum wage, if the value of a young hire is zero, then working for free to gain experience is probably necessary (otherwise no one will hire).

We have other structural issues in society that make this difficult now. For example the fact that without a large pay check, few young people will be able to live near the place where jobs are available, afford essentials, and will have no health care.

But yes, if we returned to a culture of "children live with parents until married" and "apprentice at a company until your work is valuable", and companies returned to "hire what you actually need, then invest heavily in employee growth for the long term", and reducing churn of employees (so that employees and employers have incentive to do this), then it might be possible.

So how do you solve the problem of the company investing in their employees to make them more valuable and then the employees go to another company to get paid more (because that company does not spend on developing employing employees) or the employees leave to start their own company to compete with their original employer?

It's moot, because it will never happen. The apprentice system worked because they could perform actual useful work, if only sweeping the floor and such. An apprentice would only slow me down. A Keurig and a Roomba would be far more useful.