Interesting observation - my 30+ years of experience includes over 400 audits in various industies, litigation support, expert testimony, forensic accounting, and in recent years digital forensics. Sorry if I bristle a little, but as an expert witness I take no prisoners with respect to my technical background and experience.
My way of "cracking the age barrier" is to find a university that will hire me as an accounting instructor, and then after I've proven myself allow me to enroll in their PhD program in accounting. Since I'm on the verge of completing degree number 3, while I'm working fulltime, I don't see why I can't do the same with a PhD. Yes, it sounds insane, but public accounting teaches discipline and focus, and If you have to work 70+ hours to get done what has to get done you do it. Part of the reason, in my opinion, that there is a shortage of accounting professors with PhD's is because colleges never caught up with the "rebound effect" from the institution of the 150 hour rule in the 90's. When it was passed in the 80's, in my opinion, it was a direct attempt to reduce the number of CPA's in public practice. Peer review/quality control was mandated in most states at the same time and consolidation in the public accounting industry has been increasing ever since. What hasn't decreased, however, is the number of students entering colleges to earn degrees in accounting.
I believe that I'm getting close to finding the right fit, but I believe that it wouldn't have happened if my wife and I hadn't gone back to school two years ago to earn master's degrees in digital forensics. We did it to enhance our fraud investigations, and found "real joy" in getting to know our much younger graduate students, and in-turn our professors. Blowing the "academic cobwebs" out was tough, but well worthwhile. My conclusion is that maybe some of the PhD programs in accounting need to stop looking at "candidate age and institutional investment" and consider real world dynamics - federal judges, politicians, business leaders, doctors, attorneys, and actors also still viable at 60+.