> in my generation, most UK students got their PhDs around 24-25 years of age; for the US students it was more like 27-28
The programs were not quite equivalent. US Ph.D. programs have traditionally included more courses and include a comprehensive examination in addition to a dissertation. A US Ph.D. candidate must demonstrate a broader understanding of the field and cannot just jump into thesis work upon starting their Ph.D. program.
Sure, they may not be identical but they were teleologically equivalent. Newly minted PhDs from both countries proceeded to compete for the same jobs on a seemingly equal footing.
The programs were not quite equivalent. US Ph.D. programs have traditionally included more courses and include a comprehensive examination in addition to a dissertation. A US Ph.D. candidate must demonstrate a broader understanding of the field and cannot just jump into thesis work upon starting their Ph.D. program.