Even though 'Toine and Pierce didn't come into the league at the same time, they were actually even closer in age than Smart and Young, and they remind me of the two:
Antoine was incredibly durable through his time with the C's and he started his career playing in every game and starting 68 of them as a 20yo. He was an easy talker and front-man from the very beginning.
Pierce was the more quiet, younger sidekick, but he came in with loads of skills at the wing and just went about his business. Pierce was two years older than Young as rookie, however, and I expect Young will take longer to emerge as a player.
The big difference I think is that Smart will have Stevens to keep him playing the right way, as opposed to Toine, who was left to develop his volume-shooter habits without constraint.