Apples and pineapples (that is wOBA and wRC+ and not isoP or HRs). And Small Sample Size bias on either size (like how many 19, 20 and 21 year olds and 39, 40 and 41 year olds were in the majors) skews the curve on both edges. I suspect that the rest of it (25-35 or so) where there is a significant sample size the variations are between the standard deviation, so all curves are identical. Unless they provide sample size (and it is significant on the edges, like p<0.01 or something), you cannot be confident with the conclusion they are reaching. All it takes is one Trout and one Harper to skew your data that way, if you have an age group size of 2.