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Put another way, Utley had OPS+ of 87 and 93 at ages 24 and 25 ... then became a superstar at age 26. (Granted, it was in 440 ML plate appearances.)
Sandberg spent three calendar years struggling, ages 21-23, OPS+ well south of 100. He needed 1,400 ML at-bats and then he exploded into a HOF'er.
Ackley has right around 1,000 PA's in the bigs, with an OPS+ (93) that mirrors the two guys you mention.
...........
We're all well aware of the "Age 26 With Experience" rule from John Benson. But those examples are somehow extra-compelling.