A couple of things...
1. You can go to the PLAYERS & FACEGEN tab to look at the player development settings and how fast you want players to develop.
2. It sounds like you might want to change your AI evaluation settings to be based more on stats. That's under AI SETTINGS. That way you can make the OVRs you see based more on stats.
As for what the actual code is for player progression/regression, I'm not sure of that. But, it's likely based on age, current skill, current potential, and some level of randomness.