And may I ask how Wookieepedia can know how old exactly Brianna is?
To me Kreia is very old. 70-80. And she is not corrupted (in her appearance) the way other people are. By the way, not everyone who falls to the darkside turns ugly. Just look at Bandon. Dooku.
In the movies, only Palpatine is "deformed" and "scarred". Dooku, Maul are not. And Vader's uglyness is due to his injuries I'd say.
Also, I doubt that when developers worked on Kotor I, they already got Kreia in their mind.