I found all the players who were primarily 1Bmen and/or OFers who had 15+ seasons with 400+ PAs and found their average RCAA at every age from 21-39. RCAA is runs created above average. It comes from the Lee Sinins Complete Baseball Encyclopedia. Here is how he defines it: “It’s the difference between a player’s RC total and the total for an average player who used the same amount of his team’s outs. A negative RCAA indicates a below average player in this category.” It is also park adjusted.
The graph below shows the averages at each age. It surprised me to see that there is no peak but a plateau from 25-29. I sure don't know why it would be like that for this group.
The table below gives the average for each age as well as the number of players at each age. Seems like a pretty stable number of players from 24-36.