The PP is correct that there are makeover options on property for those older than the BBB max age. In fact, you may prefer these as there are more options than the “standard” few choices that are offered at BBB which is geared for kids. Regarding your desire to dress up in parks, that’s awesome! Unfortunately because of the times we live in there are lots of rules that prevent teens from getting to be a kid and dress in costume, even at Disney.
BUT there’s good news that, because of your age, you may prefer over the generic costumes that younger kids wear. Have you heard of “Disney-bounding?” This is a concept where you are not directly in costume BUT you are dressed in a theme. Think “what would Belle wear to the parks? Probably not a ball gown right? But maybe something yellow and sparkly with rose accessories? (or a blue dress like her “everyday” outfit?) There is no rule that you can’t use glitter hairspray, makeup, and dress in a way that makes you feel great. There are lots and lots of online forums where people share ideas. I saw the most awesome Ursula and Arielle Disney-bounders last trip!