If I can make a suggestion, the simplest thing would probably be to simply fix everyone's age to what it should be. If the sim is based off of current MLB time (or supposed to be anyway), it doesn't make much sense to change players ages.... even with considering the league started in the "future", per se. If you're changing ages, might as well turn it into a historical league and import retired players too.
I just don't see how changing their age is really beneficial. It's no different than say, waiting until they're 40, and kicking their age back to 38 then. It's the same thing really...