His analysis gave the threshold or "mean" age of prospects at each minor league level:
| Level | Age Threshold |
| R | 16.71 |
| A- | 19.13 |
| A | 19.59 |
| A+ | 20.34 |
| AA | 21.39 |
| AAA | 22.65 |
The reason for finding a mean age at each development level help determine whether a prospect's age at current level helps or hurts that player's stock. Age is a valuable factor to use because it is factor because the average major league player's career is relatively short. It also shows a maturity factor for younger prospects handling the pressure at various levels. Age is also a factor in the level of competition throughout a prospect pre-professional career. For example, a player performing better than his older peers at one level could be considered a better prospect long term.
The average age at rookie ball would be around 17, which is high school, which makes sense. Most high schoolers do not have major competition in their team sport. Low A ball bumps up to 19, which is the first promotion for high school draft talent. This area includes short season leagues. At A ball, the age jumps about 1/2 year to 19.5, which again makes sense. High A ball (like Daytona), the age is just above 20, which would be about 2.5 years for a raw high school player or a junior college draftee. Double A is about 21 years old which would be first promotion for junior college type prospect, and for a college senior. AAA is around 23 years old, which is the large age gap because players reaching AAA may be position blocked at the major league level. But a 23 year old would be a college senior (redshirt) or senior draftee approximately 2 years in the organization.
So the average promotion path from the raw data is fairly consistent with common sense.
A rookie league prospect will take approximately 3.5 years to reach High A on the verge of AA.
An A level prospect will take approximately 2 years to reach AA. (This gives a young rookie player 1.5 years to get on track).
A AA prospect is expected to be promoted to AAA in a little over a year.
Even a general rule of thumb promotion curve of one year at each level, a 17 year old rookie would be expected (or hoped) to excel at each level: 18 at low A ball, 19 at high A ball, 20 at AA and 21 at AAA. And this is why many scouts and GMs no longer use the "prospect" tag on a player who is 24 or 25.
We get the perception that the Chicago teams are holding back their prospects in the minors. But the Cubs had four players age 23 on the major league roster this year: Rizzo, Castro, Lake and Watkins, the the former two having previous big league experience. If one argues that pitchers take longer, the Cubs had only 24 year olds make brief appearances this last season: Grimm and Cabrera.
The White Sox seem to promote quicker and more toward the norm. The White Sox had six players 23 or under on their roster this season: A. Garcia, Semien, L. Garcia, Gonzalez, pitchers E. Johnson and Webb. The White Sox also had three pitchers with a lot of major league experience: Sale, Quintana and Reed.
The often named prospects in the Cub system (mean age) and their ages:
Daytona (A/20.34): Bryant (21), Soler (21), Vogelbach (20), Baez (20), who was promoted to AA in season.
Tennessee (AA/21.39)): Ha (22), Szczur (24), Alcantara (22), Jokich (24), Ramirez (24), Kendricks (24), who was promoted to AAA in season.
It may more a factor of where an initial draft choice is placed than age with the Cubs. It may be a gambit on the Cubs number game where the shear volume will statistically produce more talent. Holding back talent in lower levels may make those prospects appear to be better (against younger competition). It also may be a tell that certain prospects hit their ceiling at a certain level and their careers stall there for several seasons, hence the older age level. So if you draft AND develop correctly, there is no reason why the Cubs or White Sox cannot move their best prospects quickly through to the majors.
