SELECT
 AGE AS AGE
 , CASE
    WHEN GENDER_CODE == '20' THEN 'MALE'
    ELSE 'FEMALE'
   END AS GENDER
FROM
 SCHOOL_HEALTH
WHERE
 SURVEY_YEAR = '2019'
GROUP BY
 AGE
 , GENDER_CODE
ORDER BY
 AGE DESC
 , GENDER_CODE DESC
;