Going back 55 years for an example tends to support the opposite point. The age of the prospect and the age of the competition are very important for player evaluation, especially if a young prospect is succeeding against older competition or an older prospect is struggling against young competition. Tearing up the Appy league says something different about a 19-yr-old than it does about a 22-year old. At 19, it says "good prospect." (For Kiriloff, is says SSS, but so far, so good.) At 22, it says "get this guy to an appropriate level of competition so we can find out what we have here." The Twins really didn't do that for Oliva until age 24 in 1963, which is part of the reason he didn't make the majors to stay until he was 25. I think his defense also held him back some, but the MiLB landscape was quite a bit different in the early 60s, and Tony O's path to the majors was unusual enough at the time to make it difficult to use him to make any general statements about prospect evaluation today.