I’m not sure what the background of the other posters on this discussion are, but I know from personal experience that there’s a girl in one of my classes in GS who’s 19 that transferred from another school. There’s also at least one person in GS now who is 17. If you have an interesting life story and transfer some credits, it is possible. You can even graduate high school early by taking a GED. That’s what I did. Just consult with one of the admissions officers at Columbia GS before applying. I’m sure they’d be happy to help you and would be able to advise you better than we could.