Canine dementia progresses pretty quickly especially since a dogs lifespan is only between 13 to 20 years depending on the size of the dog.
Dogs who get dementia usually start getting confused and may not even remember you which could become harmful to you and your family and if a dog is getting dementia where it's severe enough that the dog is becoming dangerous it's best to have the dog put to sleep.
The canine dementia or dog dementia will only get worse as the dog ages even more and once the dog has dementia they will likely die with a year or two anyway.
So for the safety of yourself, family and to stop the suffering of the dog with dementia it would be best to put the dog to sleep.
The age at when most dogs get dementia is around 10 to 12 years of age depending on the dogs lifespan.
If the dogs lifespan is around 13 to 15 years then the dog may get dementia when they are 10 to 12 years old and continue to have the dog dementia until they die.
If the dogs lifespan is around 20 years then they may get the dog dementia at around age 15 years old if they are gonna get it.
Not all dogs get dementia as they age just like not all humans get dementia in old age but dog dementia is pretty common.
If you notice your dog is getting confused or you notice signs of the dog developing dementia such as circling, wandering and house soiling then your dog likely has dementia especially if they are nearing the end of their life.
A few other symptoms of dog dementia include include lethargy, sleep disorders, decreased learning and vocalizing.