I think I have read the term "young" a thousand times over the past two days. Kinda of tired of people one guy over another because they are young and/or representing what it actually means to be young.
These guys have been playing ball their entire life. By the time they get to the league there general skill set already defined. A center isn't going to work himself into a PG (and vise versa). Is this extreme? Sure but the point is that players get better but in small doses (that can sometimes make a big difference).
A guy that is three years in the league isn't young in my eyes. Moreover, by this time, an experienced talent elevator knows what is guy can and can't be to a fairly certain degree. Sully is a case in point. I think everyone knows what he will be. Perhaps he can change the trajectory "if" he controls his weight but that is also part of the equation. What are the odds that he controls his weight? Probably not good.
So take a chance on a rookie or a second year player for their potential? I suppose. But beyond that, don't worry about age.