Faile, per the wiki, is 17 when the Great Hunt is called. Now over all this does put her three years younger than Perrin, But she is the same age as Elayne and Egwene.
As far as the relationship type I don't think it will be as problematic if they portray it differently. We live in a post 50 Shades world, after all, and a strong, independent, woman who wants to be dominated and be with a man can be assertive, and respects her enough to let her do her own thing - while being right there to rescue her if something goes wrong? Hardly a bad thing with the right lense.