The "super-young" argument doesn't really hold water, I don't think.
Walker Jenkins is the oldest, most-experienced top prospect who is still at AAA.
Here's what I mean by that: I looked at the Top 50 ESPN prospects (they just updated their list today). Of all the prospects who are as old or older than Jenkins, four are currently in the majors, eight are at AA or below and five are at AAA. Of the five at AAA, here is their experience level there -
Walker Jenkins - 86 GP, 380 PA (started the season at AAA)
Aidan Miller - 8 GP, 37 PA (started the season at AA)
Cam Cannarella - 23 GP, 101 PA (started the season at A+)
Seaver King - 49 GP, 220 PA (started the season at AA)
Thomas White - 5 GS, 81 BF (started the season at A)
No Top 50 prospect currently at AAA is older than Jenkins, with more experience at that level than he has. Even factoring in his injury time, Jenkins has more experience this year at AAA than any prospect his age. And he's the only top prospect at his age (or older) who started the season at AAA who has not yet been called up.
And if you look at the guys who are older than Jenkins and in the majors now, they all have roughly the same AAA experience (if not less) as he has had:
Max Clark - 90 GP, 418 PA (two months older than Jenkins)
Angel Genao - 72 GP, 309 PA (nine months older than Jenkins)
Kaelen Culpepper - 74 GP, 343 PA
Luis Lara - 78 GP, 346 PA (three months older than Jenkins)
It is just not the case that Walker Jenkins is "super-young." Are there older prospects still below him? Certainly. But all of the prospects his age or older who started the season at AAA are now in the majors and the only prospects his age or older who are currently at AAA didn't start the season there and have significantly less AAA experience than him.