It can be done without that level of saturation. I started taking summer school classes after 8th grade. The extra summer school credits allowed me to "skip" my junior year in high school. I continued the practice into college and finished with my BA in Biology from UCSD at age 19. I took 18 to 22 units during Fall/Winter/Spring quarters. Most summers I was able to wrangle another 16 units. It didn't leave much time for "social life", but UCSD was pretty dead with respect to "parties" in the 1974 to 1976 time frame.
Now that the young man has his bachelor's, it is time to look ahead to grad school. Hopefully, he has a good idea of where he wants to go in life. The absence of life experience could make for a less than optimal decision.
Isn't this true for high schoolers as well?
Young people who graduate from college early may not go on to make their major their life's work. If they don't, they still have a college level education in that field, and that will become part of the general education that will greatly enrich their life.
My youngest is considering becoming a physician's assistant or a nurse. She earned a B.S. in mathematics at 18. To earn that B.S. degree she needed to take all the general college courses, biology, chemistry, and physics. I consider that a very well rounded liberal education. She is well prepared educationally for whatever she chooses to do in life.