SELECT TO_NUMBER(TO_CHAR(SYSDATE,'YYYY')) - TO_NUMBER(SUBSTR('1984-04-14',1,4)) + 1 FROM DUAL;

WITH employees AS
(
SELECT 100 employeeid, 'Steven' firstname, 'King' lastname, '2003/06/17' birthdate
UNION ALL SELECT 101, 'Neena',     'Kochhar', '2005/09/21'
UNION ALL SELECT 102, 'Lex',       'De Haan', '2001/01/13'
UNION ALL SELECT 103, 'Alexander', 'Hunold',  '2006/01/03'
UNION ALL SELECT 104, 'Bruce',     'Ernst',   '2007/05/21'
)
SELECT employeeid
     , firstname
     , lastname
     , birthdate
     , YEAR(NOW()) - YEAR(birthdate) + 1 age_kor
     , FLOOR(TIMESTAMPDIFF(month, birthdate, CURRENT_DATE) / 12) age_man
  FROM employees
;