I think you're making too many assumptions about Asha's education and Knowledge base about the North. She is well travelled and her family's Leige Lord was Ned Stark....she is most likely way less ignorant than you make her out to be. You don't think she asked Maesters, or Nuncles about the people her Brother was being raised by?
Does anyone know exactly how many days are in a Westerosi year? I never put much stock into ages in the books, and always assumed that since characters seem to act much older than they are they probably are much older. We assume that a 'Name day' occurs every 365 days....but what if it's more like every 450 days? That would make a 14 year old Jon Snow closer to 17-18 at the beginning of GOT. ...just saying....