Um guia para quem estuda Inglês Online
What does "She is 13 going on 19 [age]?" mean?
She's referring to what I might say is "13 going on 30" (except she uses 19, which may be more accurate). She's saying the girl is 13 years old, but she acts or looks (or both) closer to 19. In my "13 going on 30" example, this could be a compliment or simply an observation (and you can use any numbers, really; 14 going on 40, 20 going on 40, 8 going on 80). It could be saying that the person is only 13 but she or he has the maturity, insight, wisdom of someone who is much older. In the "13 going on 19," your friend is saying the girl has the toughness of a 13-year-old but the understanding that usually comes later, as with a 19-year-old. Whether a 13-year-old is tougher than a 19-year-old is a matter of opinion, so it's not a comparison that I personally would make.