I've done this with 2 different leagues now, and I've had the same result but with different players.
Both leagues were historical imports starting in 1921 with full history for MLB and Negro Leagues and Minors imported. Everything set to import new rookies each year, auto-expand, etc. Both leagues with no human controls, me set to commish, and just sim to March 27, 2023.
In first test league, player
Frank Burt is the issue.
Historical ID burtfr01
BBRef ID burtfr01
Historical Minors ID burt--001fra
He has OSA ratings on 1/1 of each year in his history starting in 1922 to 1930, then starts signing with minor league teams every year, sometimes multiple times per year, until about 1954 when he starts playing Major League games. By 1958, he's starting 35+ games every year as a SP until 2019. Then he converts to a RP and pitches in 42-75 games each year between 2019-2022. In 2019, it shows he's 19 years old. His age showed 0 until 2004 when he turned 1. His career numbers are off the charts. He has every pitching record imaginable. His Major League Service is over 72 years.
In 2nd test league, the culprit is
John Dwyer
Historical ID dwyerjo01
BBRef ID dwyerjo01
Historical Minors ID dwyer-001joh
VERY similar story, only this time as a Catcher. Started playing MLB games in 1944, is now 19 in 2022. His Major Service is 86 years.
Happy to upload screenshots if you need them, let me know what else you want to know.