Do not sing any song that is not remotely age appropriate. A teacher who doesn't like the way you sing will hold that against you. (Remember Mr. Karp from "Nothing".)
Stars and the Moon for instance. Meadowlark is another. Ditto Stormy Weather. All of these songs need miles on your tires.
I was at a concert by Mr. Brown, and he said he was always getting requests from high schoolers to sing Stars and the Moon. He got a big laugh from the audience, half of whom were too young to sing it and they were at least 30. It would be like the movie Camp with the 16 year old singing The Ladies Who Lunch.
Did you know that The Lady Is a Tramp was written for a young woman to sing? She is singing about being a hobo I think as opposed to being free and easy. The same character sings My Funny Valentine about her new boyfriend whose name is...you got it, Valentine.
Nellie in South Pacific is only about 22. Maria in The Sound of Music is 18 at the start. Liza Doolittle is about 21.
"If my life weren't funny, it would just be true. And that would be unacceptable."
--Carrie Fisher