[One Post Wonder]

IMO the problem with leaving it as it is in real MiLB is that the AI will stack the lower leagues with 25 and 26 year old ringers, and it's hard to tell who is ready to move up because all the 18 and 19 year olds, the players you're interested in, are hitting .118 and have eras of 7. Plus they get awful morale because they're stinking up the joint, which makes them stink more.

I often do something similar to OP and it works. On top of that I'll put roster size limits on (35 for upper league minors, 40 for rookie and SA) to stop AI AAA rosters from having 60 players.

This will also help with parity in your game, since a guy not good enough to move up to AAA in one organization will be released and picked up by a weak team who can use him.

The one thing to keep in mind is that you'll need a big draft pool to get enough guys at each age bracket to fill all the teams. That or allow ghost players.