@Teruru I don't think official ages have been given, but there's a blog post (https://goldenkamuyhunting.tumblr.com/post/181664485998/do-you-have-estimates-of-the-character-ages) that estimated the ages based on info given. Asirpa is around 13 (close to marriage age for Ainu, old enough that her grandmother says she should get the face tattoos).
I can't imagine we'll get another kidnapped Asirpa arc, so Boutarou's probably not getting too far. I feel like this is setting up Asirpa to kill Boutarou. He represents her desire to live a peaceful life with Sugimoto, at the cost of betraying her people, so her killing him will represent her taking up the cause of the Ainu, and the bloodshed it entails.