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