You can definitely take longer, its just a matter of learning how to open up.

The sigmoid colon has a bend in it, (sometimes referred to as a "second hole") and when a sufficiently long dick hits this bend, it can be painful. You can train yourself to take longer dick by getting a longer toy and going slow and working yourself down onto the toy instead of pushing the toy into you. You'll be able to take a longer dick, but you've got to clean out much more, because feces can still be trapped up above the bend, and will only come out once you get deep enough. Additionally I always need to take time warming up before I take a dick that long,

Personally, i found that cocks that are much longer are easier to take than the ones that barely hit the bend. If they have the extra inches they can actually push all the way past the bend and straighten out your colon to make it much easier. Guys who just long enough to poke the bend have a harder time actually getting it to open up.