In terms of her chronological "age" within her story, Snow White remains the youngest Disney Princess, as she is canonically only 14 years old. Most of the classic princesses are teenagers, including Jasmine (15), Ariel (16), Aurora (16), and Mulan (16). In terms of the most "recently added" to the official lineup, Raya from Raya and the Last Dragon (2021) is the newest addition to the official Disney Princess franchise. However, if you are looking for the youngest "character" who is a princess, that would be Sofia the First, who is roughly 8 years old, though she is considered part of the "Disney Junior" brand rather than the primary Disney Princess marketing franchise. It is important to note that Disney has a very specific set of criteria for who becomes an "Official Disney Princess," which currently includes 13 characters: Snow White, Cinderella, Aurora, Ariel, Belle, Jasmine, Pocahontas, Mulan, Tiana, Aurora, Rapunzel, Merida, Moana, and Raya. Interestingly, Elsa and Anna from Frozen are so successful as their own standalone brand that they are not technically part of the "Disney Princess" lineup. Therefore, while Snow White is the youngest by age, Raya is the "youngest" in terms of how long she has been part of the official royal court.