Younger dog fighting with old dog

[Eightlegstwotails]

Hi looking for advise. I have two dogs both are easy going and well socialised.the older dog is 12 life expectancy for breed 10-12 he is fit and well happily walking off lead for 1 1/2 hours a day, he is going grey, his eyes are starting to cloud over and he's momentarily stiff at times but otherwise no obvious change. The younger dog is five he's fit and well. He has been with the older dog since he was 8 weeks old and up until a few weeks ago he was devoted to him, they sleep together, sit together, eat in the same room, share treats without fighting and the younger one cries very badly on the very few occasions I've separated them e.g. to take older dog to the vet.
But in the last few weeks the younger one has started attacking the older one, not very seriously at the moment, initially growling at him, then growling and snapping, now growling and getting hold of the older dogs fur and pulling lumps out. Or if the older dog is in his bed/on his favourite chairs (only room for one dog) he hassles him all the time. The older dog simply ignores him. When we go for a walk the older one has always gone ahead on his own now the younger one constantly mounts him or pulls his fur, the old dogs doesn't even seem to notice or care but I'm finding it it rather irritating.
Also when we all sit down at night the older dogs sleeps on his chair but the younger dog has started fiddling all the time, he just can't sit still, he used curl up on the sofa peacefully but now he scratches the cushions, climbs on my lap then off, licking everything; carpet, shoes, my legs, the older dog, the cat, or goes into the kitchen barking if he hears a noise in the garden (he's never barked before), or just generally hassling the older dog pulling his ears, fur, or poking the cat, snapping at the cat, it's beginning to drive my very non dog loving husband mad.
Is it changes in dog hierarchy dynamics, my husband thinks it is. The older dog is getting to old to be in charge but the younger dog half wants it but ultimately hasn't really got the bottle to do the job and is therefore stressing all the time?
Just to add the younger dog has lots of doggy friends and shows no aggression to them either out walking or if they come to our house.
Any thoughts?

Just gone into kitchen where both sleep at night they're happily curled up together but 10 mins ago the younger one was snarling and pulling the fur of the older one.

Have you taken the younger one to the vet to see if there is anything actually wrong with him , as I'd do that first.

It does sound like your husband might be right. However if your older dog isn't bothered unless they are doing damage to each other I would try as far as possible to leave them to it. Dogs have a habit of working these things out themselves.

I'd get both dogs checked out by a vet first. With any behavioural changes physical causes should be ruled out first. Feeling uncomfortable or out of sorts could be making your younger dog restless and more short tempered than usual. Equally it's possible that there's something going on health wise with your older dog that is not yet apparent to you but the younger dog is aware of and that is triggering the behaviour.

Both dogs were checked recently when they had their vaccines this problem had just started but it wasn't really registering it at the time. The vet was impressed with the old dog she said he looked distinguished with his grey and that all things considered he's "amazing" for his age. But I read somewhere ?on here that many older dogs have the equivalent to dementia, he's never been the brightest bulb in the box he eats sleeps pees poos walks and loves everyone but I wondered if he is getting even more "simple" if that makes sense. Does anyone know what the symptoms are?

My mums elderly terrier has dementia , but with him it's things like getting transfixed on things in the garden and seeming to forget how to get back inside ( or move) and he does pee indoors sometimes . That said he's definitely not simple and these things don't happen every day

Bumping for any more thoughts. x