Minhag Chabad brought in Hayom Yom is that the Chazan for Mincha or Ma'ariv doesn't wear a Talis, same for Shabbos, R"H and Y"K. (No difference between married or Bochur)
In Chabad (by the Rebbe) Bar Mitzvah boys generally don't get Aliyas Shabbos morning, Mincha they don't wear a Talis and weekdays, the Rebbe would be at the Yeshiva Minyan so the assumption is that if the Tzibbur aren't wearing Talleisim, it's not necessary for Kovod Hatzibur.
As far as Shabbos Chazan and Aliya by Shachris there are different schools of thought.
By the Rebbe, the only Bochurim to get Aliyas Shabbos morning were Chassanim by their Aufruf and they did wear a Talis. There were exceptions though. Such as a Bochur who Leined on Shabbos morning, or a Bar Mitzvah boy who got an Aliya on YT and they also wore a Talis.
Some say that whoever gets an Aliya by a Minyan which is mostly married men, should wear a Talis, and that's the only reason why a Chosson does. Others say that only a Chosson should but other Bochurim shouldn't wear a Talis even if they are getting an Aliya at Shachris in a Minyan which is mostly married men.
ETA: I wrote this half asleep and I wrote later paragraphs before earlier so it might not make sense.
I hope you find my comments interesting though.
