I have a theory, due to a bizarre phenomenon that occurs with the Transformations between Travels with the Portals that connect the Human World with the Pony World, when someone from one world goes to the other, and takes on a form that fits in with the other world, their New Forms don't allow them to Age, leaving them stuck looking exactly the same age as when they first arrived in the other world, which would explain why the Dazzlings/Sirens were still alive & teenagers despite the fact that they were over 1000 Years Old, and didn't age to dust when their amulets broke(ruling out any ideas that the amulets were the source of their eternal live & youth), so if Pony Sunset came to the Human World when Twilight was still just a Filly who had yet to become Celestia's New Private/Star Pupil after Sunset, then it stands to reason that Pony Sunset despite looking like a High School Teenager, is actually somewhere in her Late 20's/Early 30's, so her Human Counterpart(who is Not under some sort of Anti-Aging Enchantment) is a Grown Woman living her life somewhere else, now Imagine how it would be if Human Sunset took a job as a Teacher at CHS, and Pony Sunset was in her class, like "The Parent Trap" meets "Freaky Friday" am I right?