On a hunch...did you have no amateur draft? If so, it might be the same issue I mentioned
here.
The longest I simmed those two leagues was 21 years or so, and the position player ages weren't too bad at that point (although definitely on the old side, on average), but I can easily see how that might go completely out of whack with another couple decades under the belt.
I actually might still have one of those saves...I'll check later.
Edit: Yup, still got that game, but it was only simmed for 16 years after all (through 20
21, hence my mix-up). What's intriguing is that this league turned into a
pitcher's league after about 10 years when the position player resupply fell apart (4.54 ERA for 2006-2015, 4.05 ERA for 2016-2021)...I'm stunned to read that mm7607's league became a hitter's paradise, but maybe my 6-year window into the developing geezer's league wasn't long enough.