As we know, the ages of the characters on Game of Thrones can be very different from both the corresponding age in the books and the present age of the actors portraying them. Moreover, we don't really know exactly how much time has passed since the events of season 1. (This question shows that the speculated time is one year per season, but that's not definitive.)
Now, ignoring Jon Snow's parentage for the moment, there are three trueborn Stark children currently in Winterfell: Sansa, Arya and Bran. My question is, what is their current age according to the show's canon as per the latest episode (S07E07). (An approximation or an educated guess will do if the explicit age is not known. I remember Sansa telling Tyrion her age back when she was at King's Landing, but I don't remember the episode.)
It would also be interesting to know how old Robb Stark was when he was declared King in the North.