Sasuke is still "young" and has unlocKed EMS so I guess if he gets Sunju DNA he might unlock rinnegan at ayoung age.
Depends what your opinion on young is. -20? -30?
no ..i don't think so!!! It would seem possible in the case of Nagato but ...as we all know that he got his Rinnegan transplanted...so very unlikley!!!
I have no clue whether how you unlock the rinnegan on a young age but for example, Madara Uchiha unlocked the Rinnegan whe he was close to dying at an old age.