I just don't get the part about "only 24" and still a prospect. Good grief at what age do you start to worry? 25, 30? An even decent player should be in the majors by the time they are 24. IMO of course...lol.
Kind of multiple points there imo Steve. You of course want players ascending to the Majors as quickly as possible (given talent / performance / need). Getting acclimated, and moving towards whatever peak they'll reach. And while in the Minors, you hopefully want to see continued development, production up the chain as they advance, and players earning / forcing their way to the bigs.
And the longer it takes a player to reach / force his way to the Majors; yeah their potential to greatly impact the ML roster is reduced.
However, development is not linear.
At 24, he's several years away from what is widely considered 'prime.' And you've got him under long-term team control costing nothing. So, imo, there is nothing to really worry about. He either produces enough to earn his way up, or he doesn't.
But given that he's already had AA success (at the age he did) and everyone that sees him recognizes he has a usable skill set... there is more to like vs. not, even if legitimate questions exist.