I recently previously got two 3 or 4 year old fuzzbutts. The previous owner only had the basement level in the 4-level cage and had bedding which they used as litter covering the whole floor. I have all the floors in and a litter box in the corner with blankets in the bottom, but they poop on the blankets too. The litter box is a hit or miss. Is litter training older ferrets harder? i am also getting a playpen with a bottom and don't want them pooping all over the floor.

I havent' found that litter training an older ferret is any more difficult than litter training a baby.  I actually think that babies might be harder since they really have short attention spans.  

I'd limit the size of their cage to just one level.  On the floor put a bed, the litter box, their food and water.  Those things should cover the entire floor, with no free space to poop or pee, except in the litter box.  You might have to help them for the first few days "find the litter box" but then they should get the hang of it.  But don't rush to add more levels in, make sure they comprehend what a litter box is before adding levels, or you will have to start back at step #1 again.

The problem is they don't always poop in the corners sometimes they poop on the side