My question is how important is for a player to reach the bigs prior to age 25 so he can develop and grow both physically and mentally. I am of the opinion that it takes a player 3 years to fully adjust to the MLB game and become a good player. Their 3rd year is when they start to really break out. Jay Bruce is an example of this he has shown flashes threw his first two seasons, but this year his 3rd seems to be putting it together everyday.
Also does coming to the bigs at an early age 21 or 22 equate to a greater chance of becoming an all star?
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.