I in general have large pores. Like if you look at Robin William's face on the cover of 'Toys', you'll know what I mean. But I think because up until I was 16 I didn't wash my face ever (because I just didn't need to), that dirt has somehow managed to get so deep that it's unretrievable. At least not by the usual methods.
I recall when I was 17 that my pores weren't this big. I guess it's ageing.