Bo Ryan was a highly successful head coach for like 25 years before getting the Wisconsin job. And yes, I’d still consider Bo Ryan that rare outlier.
Tang is the one guy that had less experience than Underwood at 52 (that I’m aware of).
Bo Ryan was coaching for 25 years
in Division III before he got UW-Milwaukee job, where he stayed for only two years. Like, he coached at a level that literally doesn't offer athletic scholarships.
Isn't this exactly the thing you're criticizing Underwood for, except Underwood was actually coaching in Division I, and for less time?
Underwood had considerably more success and experience as a head coach at this level when we hired him than Bo Ryan did when Wisconsin hired him. Way more. If we hired Herb Magee or Dave Holmquist to be our head coach would you say they're really experienced? Hell, they're some of the winningest and most experienced coaches in NCAA history - and started young, too.
My guess is you don't even know who those guys are without looking them up, even though they're #2 and #4 on the all time winningest college basketball coaches list.