with 
  function birthday (d in date, age in number) return date is 
  begin 
    if to_char(d,'DD/MM') = '28/02' 
    and to_char(add_months(d,age*12),'DD/MM') = '29/02' 
    then 
      return add_months(d,age*12)-1; 
    else 
      return add_months(d,age*12); 
    end if; 
  end; 
select * from ( 
  with testdata as ( 
  select date'2000-12-25' as d1 
        ,date'2000-02-29' as d2 
        ,date'2000-02-28' as d3 
        ,date'2001-02-28' as d4 
  from dual) 
  select rownum-1 as age 
        ,birthday(d1,rownum-1) as d1 
        ,birthday(d2,rownum-1) as d2 
        ,birthday(d3,rownum-1) as d3 
        ,birthday(d4,rownum-1) as d4 
  from testdata connect by level <= 12 
);

alter session set nls_date_format = 'DD-MON-YYYY'

with 
  function birthday (d in date, age in number) return date is 
  begin 
    if to_char(d,'DD/MM') = '28/02' 
    and to_char(add_months(d,age*12),'DD/MM') = '29/02' 
    then 
      return add_months(d,age*12)-1; 
    else 
      return add_months(d,age*12); 
    end if; 
  end; 
select * from ( 
  with testdata as ( 
  select date'2000-12-25' as d1 
        ,date'2000-02-29' as d2 
        ,date'2000-02-28' as d3 
        ,date'2001-02-28' as d4 
  from dual) 
  select rownum-1 as age 
        ,birthday(d1,rownum-1) as d1 
        ,birthday(d2,rownum-1) as d2 
        ,birthday(d3,rownum-1) as d3 
        ,birthday(d4,rownum-1) as d4 
  from testdata connect by level <= 12 
);