What is their age?

The script below is a function for counting age:

CREATE OR REPLACE FUNCTION SPEAKER.F_Age (Dob_in IN DATE)
  RETURN INTERVAL YEAR TO MONTH IS
  --=======================================
  -- Function to counting age
  -- Version 2009 01 05
  --=======================================
  Retval INTERVAL YEAR TO MONTH;
BEGIN
  RETURN (Sysdate - Dob_in) YEAR TO MONTH;
END F_Age; 

where the input parameter is date of birth
Then in SQL*Plus try it:

sql>select empname, hiredate as Dob,F_Age(hiredate) Age from scott.emp;

ENAME     |DOB      |AGE
----------|---------|---------------
SMITH     |17-DES-80|+000000028-01
ALLEN     |20-PEB-81|+000000027-11
WARD      |22-PEB-81|+000000027-10
JONES     |02-APR-81|+000000027-09
MARTIN    |28-SEP-81|+000000027-03
BLAKE     |01-MEI-81|+000000027-08
CLARK     |09-JUN-81|+000000027-07
SCOTT     |19-APR-87|+000000021-09
KING      |17-NOP-81|+000000027-02
TURNER    |08-SEP-81|+000000027-04
ADAMS     |23-MEI-87|+000000021-07
JAMES     |03-DES-81|+000000027-01
FORD      |03-DES-81|+000000027-01
MILLER    |23-JAN-82|+000000026-11

14 rows selected.

sql>

It showed the age in year and month.