Age of the Head Coach is Not Important
The key is the next head coach's ability to bring in quality assistant coaches that can teach and recruit.
It sounds nice to bring in a young guy like Harbaugh and think he's going to be at ISU for the next 20 years. The reality is if a young coach has success at ISU he will be gobbled up by a Michigan or Ohio State. They can pay more, are on a national stage and it's easier to recruit.
ISU is looking for a guy to come in & win ASAP. If he's only around for 5-8 years thats about the most we can expect from a young guy like Harbaugh or an older guy like Mike Price. If the next coach has solid success, I would hope he has a coach on his staff that would move up to the head coaching job.