It sounds like he works well and commands respect in spite of his age. Yes experience always helps and is a reasonable assessmant. There have been great coaches who have started at that age and been successful. I don't want to look back after somebody hires him, and say damn, he would have been what we wanted.
Yeah that is a worry you never know for sure. It speaks to me that veteran guys like Callahan have respect for him. I would love to hear what they say to the question- is he ready?