I'd say it's more of his complete lack of any meaningful P5 experience than his age.
Yup. It's just part of it.
I'd say this is my biggest concern with multiple guys on the staff, not just Garrett. A solid chunk of these new guys have zero P5 experience. Some I can understand, like Wager. What he lacks in P5 experience, he'll surely makeup for in Texas connections and recruiting. But after buying in big time with Frost and Co where most had little to no P5 experience, I'd say anyone is justified in have a reasonable amount of skepticism with some of these hires.
And don't get me wrong. I'm not rooting for or predicting failure. I want it to work and hope I'm wrong. Hopefully there's a cohesiveness here now that's obviously been missing for years.