From your experience, is it possible to train a 4 yr old cat to use a litter box if he has never used it before? How do I start?

Here's the story. I have two cats. One is an indoor cat that has been living with us since his kittenhood. We had him neutered long time ago, and he has been using a litter box always. No probs with this cat.
The other cat is a half outdoor cat. He has been living with us for about 2 years now. He originally lived with my mom but she died and we took him. He never was litter trained. He'll always go outside to do his business on his own, or we'll take him outside on the leash. Sometimes we have to do it twice during the night. A little annoying! We had him neutered recently because we were pretty tired of him wanting to constantly go out, and besides he'd often catch diseases that he'd suffer from himself and also infect our other cat. Now he only asks to go out when he wants to the toilet. But we want him to become 100% indoors. It will be better for both him and us. He's very dear to me and I know mom loved him very much. So what do you think? Is it possible to litter train him now? When he asks to go outside, I pick him up and put in the litter box (separate from the other cat's one) but nothing happens. The litter is wooden shavings. Should I change it to sand maybe and then gradually switch back to shavings (it's more convenient for me)?

I'll appreciate any help!
First, you can teach anything to any cat at any age, It is never too late! Second, Does he have his own litter box? If not get him a separate litter box (even more then one, maybe one closed and one open see what he likes better) but you might want to place it in the same room at the other cat's box (just far enough where he can have some privacy), Just to set an example smell and sight can help. If he was a kitten as you know you would place him there and wait, if he has an accident ignore it (because you do not want him to connect pooing or peeing to a bad thing, it is completely fine to do it just in the right place).

What I find with cats is they are very specific with where they like to do it, and it usually happens where their smell is. so if you are not too grossed out, if you go out on a walk and he pees take a paper towl and absorb as much pee as you can and put it in a bag, back at home smear what has absorbed in the paper on the inside walls of the litter box If you can, even collect the poo and barry it in the litter box (This is gross I know I'm sorry lol!) even if you can't smell it, cats can smell things that are miles away so he will defiantly smell it

the thing is, as I mantioned they tend to do it where they last did it and how they find it is by the smell, the smell will attract him to the litter box and he might just make the connection (seeing the other cat did it in the box might help as well). Also this is a bit of a new thing but just like dogs cats react to treats, feeding him a treat when he does something good will help him understand that he is being rewarded for doing a good thing and make it consistent. so make using the litter box a good and fun experience.

Also try not taking him for a walk for awhile, close him in the room where the box is (you can hang out with him in there and play with him so he wont get scared) see if he goes even at some place on the floor, if he does that is probably a spot he feels comfortable in (this could be for many reasons maybe privacy, smell, anything) clean it up and place his litter box right in that spot! next time he will probably go to the same place but this time try waiting a bit to see when he's gonna go and right when he starts pick him up and put him inside and feed him a treat when he is done - my cat has this weird squat when he goes pee or poo so we know when its coming, try and notice what your cat does right before.

As for the litter, I would suggest using clumping clay instead of sand or wood, the wood is very unhealthy for them and can cause breathing problems, also it is very unclean and can get stuck to furr and is pretty hard to clean, I personally am really against wood even for rodents I had rabbits that I litter trained and even for them I used clumping clay. For the cats as well it is less harsh on the feed it absorbs everything ! if he pees it just hardens and you can just scoop it out no smell no mess no nothing ! and cats tend to like it a lot more because it is oderless (cats hate bad smell) and doesnt stick or anything so I would suggest trying it out. If you still prefer the wood for any reason that perfectly fine but maybe try starting the training with clumping clay just to make it easier on him.

this link might be useful as well - http://www.cathaven.org/printpages/litterbox.htm

Good luck!