For your audition, the nocturne will be fine, same as the etude.
I agree that late Beethoven does not typically show well on younger pianists. That being said, late Beethoven played WELL and with MATURITY does show very well and is very impressive to listen to, especially by a young pianist. From a musical standpoint, Op. 90 can almost be considered a transitional sonata between Beethoven's late and middle styles. Many young pianists can play this sonata well, as it does not require a much musical maturity in the interpretation. The first movement is impressive, and the lyrical second movement is heavenly (literally and figuratively) when done right.
As a side note, I do know of some people who have applied to Curtis (I don't know if they were accepted, but they ended receiving "better" offers from other major schools and went there instead. I think your program may be a little bit on the "easy" side, considering that Curtis does not have a pre-college program and you will be competing for acceptance with college students. Most of my friends who have applied played works such as Beethoven's appassionata, Ravel La Valse, Chopin Ballade No 1, Kapustin Etudes ...etc for their audition. I am not sure how your program will hold up to these more "heavy-weight" programs.
Best of luck