Originally Posted by YooperBrew
Well, it doesn't keep fermenting so it really isn't more bitter. BUT, as the hops flavor and aroma fades, the bitterness becomes much more noticeable. That's why IPAs are usually better fairly young. The hops nose fades with time, leaving the IPA tasting more bitter with less hops flavor and aroma.
I think in one of the "Jamil Show" podcasts, they mention that flavor/aroma drop off rather quickly, but that bitterness will drop out as well albeit more slowly. So, if you wait even longer, the bitterness may come back "under control" (though you'll end up with not quite an IPA I suppose)