Hi, I don't think it's too late to litter train your puppy. He is still pretty young and new to this, so I think your ok.
I think it is better to have one designated spot to use as the "toilet area". A dog cannot generalize and know he is allowed to pee in several different rooms but
only on the pads. The message you are sending him is that it's ok to pee anywhere in his "den" pad, floor, rug, ect.. makes no difference to him. (the "den" being your home). By designating one area, then you are eliminating that area as the "den" and he should be able to catch on that it's only ok to go in that designated area. For this reason, it's better to pick an area that is out of the way of your living area; like the bathroom.
Here is a site that would help you to learn about litter box training.
http://www.kturby.com/litter/litter.htm