After all, the toy breeds have the longest life expectancy. Besides there being a general slowing down in a toy's later years there are also a few diseases worth mentioning. Most old dogs will have some degree of deafness and blindness. All dogs do adjust to this. Deafness will usually manifest itself as disobedience and a disinclination to bark.
Blindness is a little harder to pick.
I know many owners who think their old timer can see fairly well when in fact the vet has said the opposite. This shows how well dogs compensate for loss of vision. Arthritis is another condition most old dogs suffer from. Aspirin will relieve pain on bad days. Heart failure may present at first with a deep cough.