如果该值存储为DATETIME数据类型:

If the value is stored as a DATETIME data type:

SELECT YEAR(CURRENT_TIMESTAMP) - YEAR(dob) - (RIGHT(CURRENT_TIMESTAMP, 5) < RIGHT(dob, 5)) as age 
  FROM YOUR_TABLE

在考虑leap年时，不够精确:

Less precise when you consider leap years:

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