The reason trebles are able to sing that high is because their vocal chords are not fully developed. Shorter vocal chords mean that the notes produced are higher.

In relation to "oggie"'s comment that boys who force their voices as they get older and their voices begin to break, I was in the school choir for five years and I knew a boy called Harry who insisted on singing soprano and got extremely upset when his voice broke. Before too long he had more or less lost his voice (which had become a fabulous tenor). Mind you, I didn't give him any sympathy!

Hope that's helped.

Kat