The Seventeenth Shard is an organization of Worldhoppers from within the Cosmere Books, including Temoo (i.e., Galladon from Elantris), Thinker (Demoux from Mistborn), and Blunt (or Vao/Baon from the original White Sand). The point of the Seventeenth is nonintervention, due to Frost's direction. There are likely tiers to the hierarchy, since Frost doesn't leave Yolen, but he's directing everything.
Aslydin is in the Seventeeth Shard ... . I've given subtle clues about her before, but the ethnicity of the name should strike you.
(Aslydin is Demoux's love interest from Mistborn: The Hero of Ages, Chapters 80 and 81. Although she doesn't have a single line of dialogue in the original trilogy, she was hanging out at the Pits of Hathsin, and Demoux fell in love with her.)
Sanderson has talked about how Hoid hasn't lived through all the years through which he has existed (i.e., he's skipped forward in time in some fashion). Its possible that Demoux - and other members of The Seventeenth Shard - have done something similar. Further, it might be that the time dilation is a side effect of Worldhopping and/or moving between Realms. (At the end of Words of Radiance, Jasnah seemed surprised that so much time had passed between her 'death' on the Wind's Pleasure and her return to the Physical Realm.)