Re: Advantage of a sub age 25 MLB player..
Some players adjust very quickly. Here are the 20 year old lines for my favorite, all-time Reds, Pinson and Robinson.
Pinson: .316/.371/.509/.880, with 205 Hs, 131Rs, 47 doubles
Robinson: .290/.379/.558/.936, with 38 HRs
I say you bring em up when they can play.