Four years ago I did a study of 165 all-stars and super stars to determine at what age they reached certain levels of the professional baseball system. I found that the median age (50% at that age or older and 50% of that age or younger) was as follows:

Major Leagues - 23
Triple A         - 22
Double A       - 21
High A          - 20
Low A          - 19

Low A is as low as I went because so many college guys started at short season ball it muddled the system pretty bad.

I tried to avoid the cup of coffee situations such as Breyvic Valera's 2 game stint at Springfield this season, even though he aquited himself well there and Mike Shildt said that he played like he belonged.

At the various levels the following prospects were at the median ages or younger:

Major Leagues (Age 23 or younger)
Adams, Cleto, Rosenthal, Miller and Sanchez

While Cleto, Miller and Sanchez pretty well fit the cup of coffee situation, Cleto and Sanchez reached the majors for the second year and Miller while cup of coffee in the regular season pitched some meaningful innings in the post season

Triple A (Age 22 or younger)
Only Miller and Rosenthal met the criteria

Double A (age 21 or younger)
Martinez, Taveras, Wacha and Wong

High A (age 20 or younger)
Vargas

Vargas was at Palm Beach for only 7 games and that probably would go down as a cup of coffee. However, I think he could have stayed there. He is a plus defender and hit .364 in 26 plate appearances. Unfortunately he had to go to Johnson City to get regular play as he was in the pecking order behind Wong, Starlin Rodriguez, Luis Mateo and Valera, all of whom were selected as all-stars in their league.

Low A (age 19 or younger)
Jenkins and Llorens

Approximately 40% of the stars were a year or more older than the median age when they reached the respective level. So even though a player was a year older than the median age they still had a 40% chance of being an all-star.

The Cardinal prospects that were one year older than the median age were as follows:

Major Leagues (Age 24 or younger)
Kozma, Jackson and Kelly

While Jackson's activity represents a cup of coffee he was in the majors for over a month.

Triple A (Age 23 or younger)
Gast, Rondon and Blazek

Double A (Age 22 or younger)
Richard Castillo, Greg Garcia, Siegrist, Whiting, Ferrara and Wright

High A (Age 21 or younger)
Miranda

Low A (Age 20 or younger)
Roberto De La Cruz and Anthony Garcia

Below Low A some of the prospects that were younger than most players in their league were

Valera, Ben O'Shea and Ben Freeman at Batavia
Kelly and Bean at Johnson City
Peoples-Walls at the GCL

As a side note in previous seasons, one of the prospects who consistently was at or below the mean age level was Donovan Solano who left the Cardinal organization as a 6 year free agent after the 2011 season. In 2012 Solano hit .295 in 316 plate appearances for the Marlins.

I am not suggesting that all of the above will be all-stars. However, many of them have a better chance than those who are a couple or more years off the median levels listed above.

Sooner....interesting data, thanks for the effort.

"Approximately 40% of the stars were a year or more older than the median age when they reached the respective level. So even though a player was a year older than the median age they still had a 40% chance of being an all-star."

You realize though are two totally different things dont you?

Thanks sooner!