In my teens I worked with the statistics department at UTMB. That had a cast of characters there; many profs in the 70s and 80s, who'd gotten their degrees before WW2. A number of them had schooling of the form: Start school at 9-10, do 5 years of public school, got to a 1 year prep, do a year or two of college, do a two year PhD. Most of them had their PhD's by 22.