A skateboarder is a person who rides a skateboard: a short board with two small wheels at each end, which you stand on and ride for fun or as a sport. The -er ending points to the rider, not the board itself. Skateboarders push with one foot, then glide; they also jump and slide on ramps, rails, and rails in parks or in the street. Some do it as play after school; some compete. The word is ordinary and modern — fine in casual talk and in sports writing. You can say skateboarder for any gender.