For years fulltime profs number &lt; 25%.
This article (with refs) shows that essentially all tenture-track professors are over 60:
<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Professors_in_the_United_States" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Professors_in_the_United_State...</a>