Before the great depression, instead of going to college after completing high school, students went to college when they were ready. The expectation to stay in high school until the age of 18 was created to shrink the workforce and artificially reduce the unemployment rate. Not long after, Robert Maynard Hutchins, President of the University of Chicago, began promoting early entrance to college for students who were ready.
The first dedicated college was SImon's Rock College, where entering students are typically about 16 years old. They earn a Bachelor's degree in four years. 78% of graduates go to graduate school. (I was one). The current wave of early colleges started about ten years ago. They are imitations of Simon's Rock. Several of them are run by former Simon's Rock staff. Some of the start-up money came from the Gates Foundation, which is not exactly the same as Microsoft.
In my view, the purpose of early college is to create an environment where young people are free to learn. For me, this was a big improvement over high school.