This is part of a larger ongoing battle between the desire of some college educated types to extend education further and further into the 20s and 30s and the desire of different college educated people to speedrun the system in order to enter the workforce and start making enough to have a family relatively quickly. It’s more of a culture clash than a clash of the sexes (though there are some sex-linked aspects).
But it’s also in a strange way a return to pre-1970s standards, where time to PhD completion was a few years rather than a decade. That increase in time happened during the 90s and has been sliding downwards back towards those older historical norms of around half a decade, driven mostly by the increase in STEM PhDs, which were frequently majority under-30 even back during the 90s and early 2000s.
In any case we’ve gone from perhaps 1 in 200 PhDs being awarded to someone under 25 to about 1 in 100 (source: NSF) in the course of the last decade (closer to 1 in 50 with STEM). And the shift is away from PhDs being awarded in the middle 30s and also away from midcareer late 40s PhDs (dominated by education majors). And yes, without education majors getting those midcareer PhDs we would very likely already be seeing a bigger percentage of PhDs awarded to the youth because STEM PhDs are getting younger more swiftly than the other PhD categories and are taking up a hefty share of the total.
And among under 25s being awarded a PhD, everyone is pretty much the same. There’s no conventional race gap among the different large-enough for reporting racial groups getting PhDs under age 25.
Anyhow, the long and short is that PhDs are taking less and less time to get, it’s not clear if we’ll keep seeing increases in the overall number (there’s been a lot of flattening out) and there’s definitely another subculture forming of extremely young but highly credentialed types, similar to what we got during the 1990s and 1970s. History sometimes skips like a scratched CD.