Cradle to Grave American Baseball System Template
This is something I've been trying to do in OOTP for years.  But this template will evolve over time to let simmers follow players from freshman year of high school, through travel ball, into Juco & college, summer college ball, and up through the minors to Major League Baseball.
When the template is done, you should theoretically be able to simulate every organized, competitive game of baseball a player plays after the age of 13.
May god have mercy on your systems.
Version 0.1
OOTP 23 default MLB system.
College Baseball:
NCAA D1
NCAA D2
NCAA D3
NAIA
Canadian college team, British Columbia ThunderBirds and Virgin Islands Buccaneers included in the NAIA
Juco Baseball:
NJCAA D1
NJCAA D2
NJCAA D3
CCCAA
NWC
High School Baseball:
8 regions, based on American Legion baseball regions
10 teams per state
20 teams for Arizona, California & Texas
10 teams for Washington, D.C.
10 prep school teams
Canadian teams from British Columbia (supplement the Alaska division)
Canadian teams from Saskatchewan, Manitoba & Ontario (an additional division in the north with Minnesota, Wisconsin, etc)
High school teams were picked by taking the top 10(or 20) schools based on the most recent available state rankings on maxpreps.com
League Reputations:
Colleges
NCAA D1 - 10(max)
NCAA D2 - 9
NCAA D3 - 8
NAIA - 8
Juco
NJCAA D1 - 7
NJCAA D2 - 6
NJCAA D3 - 5
CCCAA - 5
NWC - 5
High Schools
High school regions are ranked by 2's; 10, 8, 6, 4, based on the general strength of the region.  IE: Western with California, Arizona & Texas is 10.  Northern with Manitoba and Minnesota is 4.
Roster Sizes:
All college & Jucos have a 30-player roster + 15 reserve.  Closest to NCAA roster rules as I could get.
High schools have a 22-player roster + 22 reserve ("JV").  Again, closest I could get to "real world" equivalents.
Player creation is turned off for all college & juco leagues.
Roster rules in high school limit foreign players to 5, based on team nationality (simulates foreign exchange and immigration).
Schedule Lengths & Start Dates:
Colleges start in early February and play a max of 60 games
Jucos also start in early February and play a max of 55 games
High Schools start between late February and early May, based on region's general weather (and information found on HS baseball websites), and play 40 games.
All-star Games are turned off for all college, juco & high school leagues.
Post-season is turned off for all high school leagues.
Version 0.2
Added Arizona Fall League
Edited NCAA Division 1 to audit tames & nicknames.
Added stadium names for NCAA D1 teams
Added Team Region & Draft Region for all NCAA D1 teams
Version 0.3
Deleted summer college leagues (did not cooperate with college feeder leagues)
Audited all 8 high school regions.
Team nicknames added
Added Team Region & Draft Region for all high school teams
For Prep School division, all teams set to "All of USA & Canada" for region & draft region
Version 0.4
NCAA D2, D3 and NAIA teams audited
Accurate team regions set
Accurate team cities set
Persisting issues:
Load time remains a nightmare (dependent upon, of course, your system).
Generated players in high school teams still ignore team & team draft region upon creation.
Some AIO logo files don't automatically pair to team (teams with special characters, or schools where AIO & I disagree on which version of the school's name to use)
Download the v.0.1 file:
https://drive.google.com/file/d/1i2H...ew?usp=sharing
Download the v.0.2 file:
https://drive.google.com/file/d/1AKh...ew?usp=sharing
Download the v.0.3 file: 
https://drive.google.com/file/d/1YrF...ew?usp=sharing
Download the v.0.4 file:
https://drive.google.com/file/d/1g4D...ew?usp=sharing