How can I "fix" old walking shoes.

halfamo

You may be able to stitch them.
You can get stitching awls for the purpose and waxed threads.
There are kits available and if you can be patient enough to wait for them to come from china, they can be very inexpensive.
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There does need to be enough material left to push the metal part of the awl through and then you can push it through the sole to anchor the top to the bottom.
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I've done some like that before (hubs expensive running shoes).

DullGreyGuy

Katiehound said:

I've never found anything to mend shoes sadly.

It depends very much on what they are made of, what the damage is, where it is and how invisible/visible you mind it being.

Leather shoes that have been properly stitched together can certainly be repaired, potentially invisibly but not automatically. My loafers are on their second sole (goodyear welted so an invisible replacement) and have reinforcements to the top/back of the heel where they had been rubbed down over the 6 years of wearing before replacing the sole. This sole is probably 75% through its life and when they are gone they'll be replaced again and the reinforcement probably removed and replaced. 

Reinforcement is not invisible but with the drop of trousers covering and it being black on black its not a sore thumb either.