He still hasn't really had a major opportunity for extended minutes. We've seen players under Ainge's tenure having a couple redshirt years only to develop into rotation players (Perk comes to mind), but we've also seen some mid-to-late 1sts develop into nothing.
I don't blame Young totally for the lack of minutes. We have a lot of decent players getting minutes on this team. All four of the prospects (Young, Rozier, Hunter, Mickey) were clearly going to spend the bulk of time in d-league this season. But by year 2, you'd kind of expect Young to be getting a bit of time. Perk only played 9 minutes per game for 60 games in his second year, so there's still some hope he'll follow that path and be ready for bench minutes next year, right?