You know how in any group of friends past high school, you’re going to have most be around the same age, a couple who are quite a bit older, and then one or two that are significantly younger? That’s how I view Starlight. Like, she’s the 19-year-old friend in the group that’s mainly 22 or 23.
I think most fans got the impression that Starlight is older than Twilight because of her old hairstyle and her voice, but from the way she was written prior to Shadow Play, she always struck me as being this young prodigy who somehow started her own cult and established a little village. She’s powerful, but just very naive and carrying a boatload of issues from childhood.