Artist’s description from DA:

I finally got the time to do some headcanons! I’d Like to try doing a version of all of the mane six, with at least three versions each. A filly version, the version we have for most of the show, and a post-show older version. Twilight get’s an extra because she’s a pretty perfect pony princess, and nobody else changed species halfway through the series. So you get a filly version, a unicorn-adult version, a post-ascension version, and a version taking place after the show, with Twi fully mature as an alicorn and grown into her power.