For what it's worth, the path to American professional sports is evolving continually, and does not NECESSARILY include college.
In baseball, for example, many top American prospects sign their first pro contracts straight out of high school. Many choose the college route, but comparatively few of those stay four years.
In basketball, college if a mere formality for the best (one-and-done) prospects. Some H.S. kids now actually begin their pro careers with European clubs, rather than spend a year in college.
Football is the best example of college offering a de facto minor league system, largely due to NFL draft rules negotiated as part of the league's CBA.
Most North American kids in the NHL played at least some Major Junior hockey, mixed with college hockey. But again, the cream of the crop is entering the league in their teens.
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To bring this back to the thread, I would point out that soccer's adherents are way too quick to consign "prospects" to the scrap heap in their middle or late teens, when every other professional sport recognizes the potential for development in later years.