Younger cohorts are no better educated than these soon-to-retire boomers. Broadly speaking, educational quality has topped out - and on at least one measure, it is actually deteriorating. In 2006, Americans aged 55-59 collectively possessed more masters degrees, professional degrees and doctorates than Americans aged 30-34. This impending loss of educational capital is entirely outside the country's experience.
I cannot read a story like this without thinking in terms of assortative marriage. My guess is that most of the younger (aged 30-34) highly-educated folks are children of two highly-educated parents. My guess is that many of the older (aged 55-59) highly-educated folks are children of a college-educated father but not a college-educated mother.
I don't think we have a recipe that says, "Take a child of two non-college educated parents, add primary education ingredient X, bake, and out comes a college-capable high school graduate." The mystery ingredient X has yet to be discovered.