SQL

mysql calculate age

SELECT DATEDIFF(CURRENT_DATE, STR_TO_DATE(t.birthday, '%d-%m-%Y'))/365 AS ageInYears
  FROM YOUR_TABLE t 

mysql get age from date

SELECT YEAR(CURRENT_DATE)-YEAR(t.birthday) AS ageInYears
  FROM YOUR_TABLE t 

mysql age by birthdate

mysql> SELECT DATE_FORMAT(FROM_DAYS(DATEDIFF(now(),YourDateofBirth)), '%Y')+0 AS Age from AgeCalculationFromDatetime;