AGE function

When I execute this statement : 
select AGE(TO_DATE('20041101','yyyymmdd'),
TO_DATE('19991201','yyyymmdd'))

at postgre 7.3.3, the result :age                   --------------------- 4 years 11 mons 1 day 

at postgre 8.0.3, the result :age             --------------- 4 years 11 mons 

My question : 
1. How does postgre 7.3.3 calculate AGE function? 
2. Why the result produced by postgre 7.3.3
is different from postgre 8.0.3 ?

Thanks,
Louise

    
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