The Brands will be 54 in April, John Smith 57 in August. Gable was 49 when he retired from Iowa I believe.
Ryan Morningstar will be 36 in June. Don't know if they'd hand the reins over to Ryan when they're done, but possible I suppose. Of course Spencer Lee with his accomplishments and personality is waiting in the wings, but who knows if he wants to Coach, or how long his international career will last given his injury history, or even if his health is good?
IMO, IF Spencer Lee wants to Coach, you give him the job the first day he says he wants it. Best scenario would probably be the Gable route, Assistant for a couple years and then off we go. You can't let him get away if he wants to Coach College Wrestling. Period.
If he doesn't want to Coach you have plenty of options inside the Program or otherwise. This job has a lot to offer and will when Brands is ready to step down.