At a young age they will probably develop faster in the minors. The downside is if you leave them there too long you will ****** their development. I sort of look at their age and ratings. If I have a young guy who is like 4 or 5 in AVG I will bring him up. For a pitcher I usually look for the same level but for ERA. Once they hit around 25 I look for at least a 5 AVG or better and at least a 6 ERA or better. Sometimes you will find a really good young guy who has like a 7 or 8 ERA at age 22. However, in my experience some of them will really have tremendous careers while others will head straight down rapidly; the quick flash in the pan. Hope that helps.
Tarkus