A boy can sing treble until he reaches puberty. At puberty he starts to become a man and his voice range will go down (we say that his voice “breaks”). He will then become a tenor, baritone or bass, or he may even train to be a countertenor. A girl’s voice also changes when she reaches puberty, but the change into a grown-up female voice is more gradual than with a boy, and it is still within the soprano or alto range.