I suspect when some famous architect (who isn't supporting his kids in the family biz) decides he is designing his last one before retiring, he could probably advertise that and double his fee.
Maybe TD will do that sometime after starting his 49th course
! He could, at least.......Only trouble in marketing that is that many rock bands have supposedly retired, only to make a comeback reunion tour a decade or less later. What would stop the gca? I vaguely recall JN once said he would only design one per state (or region) but soon had to drop that as the offers came rolling in.
And the reality is, our generation hasn't saved much for retirement. And, some who did, gave it back to stay in this glamourous biz from 2009 until now. Many architects I know (and I know most of them) say they will work until they are 70-75 because they have to. (not much different than other professions/jobs/trades these days)
While I can retire, what would stop me from doing a course now and then, while my health is good, if an old client calls me out of the blue? Of course I would do it (providing it was fun the first time).