Surfing is a surface water sport in which an individual, a surfer, uses a board to ride on the forward section, or face, of a moving wave of water, which usually carries the surfer towards the shore.
Sexy is an adjective to describe a sexually appealing person (or thing), primarily referring to physical attractiveness.
A girl is a young female human, usually a child or an adolescent. When a girl becomes an adult, she is accurately described as a woman.