Please help !!!

I have a 16 year old cat. He has always been bad at peeing on dirty clothes left on the ground sometimes clean linin.
But now he has in the last weeks, he is now pooping is various places in the house.
Today he peed in the middle of the kitchen, he later popped in the den behind that kids toy box and then later in the evening he popped on the stair to the den.
His kitty litter is cleaner than It has ever been. And it is un sented and since as have more than one, we have 4 litter boxes.

How can I keep my cat from keeping up with his new idea of pooping and peeing all over the house.

My husband thinks that he is just old and is perhaps at the end of his time unless I can convince him there is someway I can figure out a) why he is doing it and how to get him to stop

Sometimes when they pee or poop in unusual places it means there is something wrong. The age is also something to consider. Did anything change in the household? New members, new furniture? I would take him in to the vet for an exam. Sometimes when cats do this they are trying to tell u something. I hope this gets resolved quick.

What are your litter boxes like? Are they open or closed? Is the entrance open low or does your kitty have to step over something? 

He's an aging cat, so like @Miso and Puma  has suggested, a vet visit is recommended. Some senior cats have difficulty moving around like they used to, so it might be uncomfortable for him to step over a tall entrance to a litter box. You might consider finding a box with an opening that is pretty much ground level. 

Nothing in the house has changed and nothing of our daily routines have changed. We have 4 litter boxes in the house as he has a brother that is also 16 and a brother that is 6. We have two that ads fairly low to the ground to step in and two that are higher to step in. He has in sented litter and it is cleaned regularly.

I am hoping what is trying to tell us is that this time as come and he will be leaving us

I think the first thing you should do is get the vet to check him over. Litter box problems are a sign of urinary tract problems and a whole range of other health issues.

16 isn't that old, he should have many more years ahead of him yet.