age() function usage

["Marcin Krawczyk" <jankes(dot)mk(at)gmail(dot)com>]

Hi all. I am trying to determine the way to pass a variable/field value to an age() function, query looks something like:

SELECT age(timestamp data_zakonczenia_fakt) FROM kip_pracownicy_umowy WHERE id_pracownika = 8

data_zakonczenia_fakt being char column equal to say '1993-11-30'.
Such approach won't work, can anyone tell me the way to do it?

SELECT age(timestamp '1993-11-30') works great.
Same story with age(timestamp '2008-01-01', timestamp '1993-11-30'). 

Thanks in advance
mk