Most MLB superstars either don't play in AAA or spend very small amount of time in AAA. They jump from A+ or AA to the majors. Trout, Harper, Strasburg, Verlander, Cabrera, Kershaw, on and on.
Average age of a MLB Player = 28.6
Average age of MLB Rookie = 24.5
Average age of AAA Player = 28.2
Average age of AA Player = 23.8
Average age of A+ Player = 22.4
Average age of A Player = 21.2
Average age of A- Player = 20.9
Average age of Rookie ball = 19.4
Hence why the assertion that by the time a player is 25, he pretty much is what he is without some huge mechanical change. AAA is were you find the organizational fodder. 31-year olds trying to hold onto their dream...Alex Presley, Efren Navarro, Arecenio Leon. While it is possible to see a future MLB superstar spending a full season at AAA, it is very rare. Additionally, anytime you see a player repeat seasons of AAA (Moya, Collins, JaCoby Jones, etc), their odds of being a useful MLB player greatly reduces the more time they spend in AAA. It also isn't a good sign when a player repeats AA, or even A+.
So when a "prospect" list shows Mike Gerber (25) as a Tiger's prospect and he hasn't even spent much time above AA, we know there is concern. It means he played the lower levels at advanced age. Or even Myles Jaye. How does 25-year old Myles Jaye still be considered a prospect? Because the Tigers system is void of worthy additions to the list. And when they trade from Dawel Lugo, people are giddy. Yet, by most career paths, he should be full time in MLB in 2018 or at least 2019. And I doubt he is "ready" by 2018 and certainly questionable for 2019, when he will be almost 25.
Anyways, I would guess that less than 10% of a AAA roster are considered "true" prospects. Where most on a AA Roster are.
