Curious age() behavior

Maybe I'm just overlooking something really simple but this has me a bit
confused.

What I'm trying to do is get the amount of time from A to B -- I thought
age() would do just that but it seems to be about a day off sometimes.

hhs=# SELECT age('Sun Dec 03 08:00:00 2000 EST','Tue Oct 10 08:00:00 2000
EDT') as esec;
esec
------------------------
@ 1 mon 24 days 1 hour
(1 row)

Ok, but if I turn right around and add that value back , I get :

hhs=# SELECT ('Tue Oct 10 08:00:00 2000 EDT'::timestamp + '1 mon 24 days 1
hour'::interval);
?column?
------------------------------
Mon Dec 04 08:00:00 2000 EST
(1 row)

Like I said, perhaps I'm blind and can't see what's happening here but
shouldn't that be Sunday the 3rd of December?

Thanks!

-Mitch