That Wikipedia page is the most hilarious wtf I have ever seen. I did not see this "< 25%" number you mention, but I read that "In 2011, a survey conducted by TIAA-CREF Institute senior researcher Paul J. Yakoboski estimated that 73% of professors with senior tenure ranged between the ages of 60 and 66 and that the remaining 27% were above the age of 66."

Then I read the reference and it said "To this end, the TIAA-CREF Institute surveyed full-time college and university faculty age 60 and older regarding issues related to whether and when to retire." The survey is about seniors (in terms of age) because TIAA-CREF is a retirement account company, not "senior tenure" whatever that means. I'm actually more surprised that the number of professors over 60 is not 100% since that's the only population surveyed.

The rest of the Wikipedia page is similarly biased, "Today (2015), adjunct professors, hired for their low cost only, rather than expertise, make up more than half the teaching faculty at United States universities." I can't tell if the Wikipedia article is intentionally ridiculous or if it's some parody article.