Nu Ralik

Probably needs a separate topic, but this leads me to something I was thinking about: How old the characters are. Shallan, for example is presented as a quite young woman - I thought 16 was mentioned somewhere, but the Stormlight Archive states she is 18 at the end of WoR. So this works out about 24.5 years old in our terms (18 x 500/365). How we view someone who is 24-25 does not mesh with how I perceive Shallan to be written. Any thoughts, comments on this?