I would think it would be relatively simple to re-train to a puddle pad, and lots of good suggestions already mentioned. But, regarding the toys, he is 6 years old, and while a lot of dogs are still really into toys at 6, some are not into toys past some much earlier age.
My Yorkie-Poo years ago quit being interested in toys not all that long after he quit teething. I worried at the time we found that tiny lost freezing baby because my sister, who is 7 years younger than me, was a baby and had toys everywhere and I did not want him to chew them up while I was in school. I needn't have worried. Instead, he chewed up one of my favorite little ankle-high boots,
so I gave him its mate when he'd chewed it down to a 'silver dollar' sized chunk of heel...but he was all done teething by then. He played only with me and not with toys...he was extremely human-like and not dog-like except for a few behaviors.
Brody, one of my two current Yorkies,
loves toys and is
extremely toy centric...I can
'see' him years from now walking with a cane, toy in his mouth...
Mia, however,
likes toys but likes taunting Brody with the toys better.
Mia prefers human interaction, where Brody prefers humans with him
and his toys. Mia will play with me and a toy, or just me, but will walk away from the toy, or give it up to Brody easily and quickly. It is nearly impossible to pry a toy from Brody's mouth to this day. Both will be 3 years old in March.
When I got Brody, he would hoard his toys and NOT play with me AND his toy...it was keep-away-tug-of-war. I think it was because at his former home, he had a 95 lb, 1 yr older canine brother when they got him, and to keep him safe, he stayed in a closed room alone during the day, with his toys, food, water, etc. I got him at 14 months old and after seeing his toy centricity, I worked with him to reduce his desperate need to have the toy all to himself and now he prefers to play with the toy while deliberately taunting me with his toy, and playtime is more fun for him. He still gets frantic when his toys are removed for washing, bedding changes, etc., but is more comfortable now with the fact that he will likely get them back again.
Perhaps you could reverse it a little, introducing him to a few toys, and reward him for a bit of play. He may never be a big toy freak, but maybe if you find the '
right' toy...one he finds interesting...he may yet surprise you.