Shortcodes not working

This is how your shortcode should be set up:

function short_birthday( $atts, $content = NULL ) {
    extract( shortcode_atts( array(
        'year' => 'default value'
    ), $atts ) );

    list( $Y, $m, $d ) = explode( "-", $year );
    $data = date( "md" ) < $m.$d ? date( "Y" )-$Y-1 : date( "Y" )-$Y;
    return $data;
}
add_shortcode( 'birthday', 'short_birthday' );