I haven't read the book, so I can't really comment on that part of the discussion. But as far as the quote above, I agree, and much of what you said has been the experience in our family.
An early bachelor's degree and youth did not hinder employment opportunities in a professional field at the age of 18 for the two of my children who did this.
So, I am sharing this to encourage anyone who is reading and has children who have chosen an accelerated path. I had my worries about this (how difficult finding and transitioning to employment would be), but I shouldn't have. The early start turned out to be a blessing instead of an impediment.
However, early college graduation was their goal and not something that I required. At times, truth be told, I suppose that my preference would have been to slow them down and keep them young a while longer, but that would probably be as wrong as pushing them would have been.
Thankfully, this has worked well for my children. But I don't push what my children have done on others. There are so many different ways to do this, and everyone has to figure this out for themselves.