MySQL Konvertera sträng till datum Beräkna ålder och ordning efter ålder

SELECT  EXTRACT(YEAR FROM (FROM_DAYS(DATEDIFF(NOW(),STR_TO_DATE(birthday, '%m/%d/%Y'))))) + 0 age,
        COUNT(*) TotalCount
FROM    tableNAme
GROUP   BY EXTRACT(YEAR FROM (FROM_DAYS(DATEDIFF(NOW(),STR_TO_DATE(birthday, '%m/%d/%Y'))))) + 0
ORDER   BY TotalCount DESC

• SQLFiddle Demo