Josh_v02 pointed out this link in Talk Sports, and I think the data in it are what Markus should use for the aging alogrithms in OOTP7.
MLB Age Factors by tangotiger
Using these is a much more accurate (read: realistic) way to model improvement and decline than what is in use in OOTP6. For example, notice that "taking walks" continues to improve with age for real players--but in OOTP6 I'd wager that isn't the case.
I'm sure that stealing ability in OOTP doesn't decline fast enough for most players either. I also wonder if avoiding K's peaks out at 27-28?