My dog is a rescue, so I don't know how old he is (I know within a 2-year range, just not the specifics). I asked my vet how I'd know it was time to move him to senior food, and she said to look for signs that he was aging -- less active, less mentally alert, worse digestion. So I'm waiting until his current food doesn't seem to be working.

That said, my previous dog developed kidney disease as an old guy, and the kidney food was either unpalatable or too fatty (the calories have to come from somewhere), so I decided it was better to shorten his life a little than to have him spend his final months hungry or laid low by diarrhea.

If he’s at a health weight and moving well, I wouldn’t worry about it.

He's 14. Let him eat what he likes. I don't think that it will make much difference as long as you are feeding a nutritionally complete food.

My 14 year old dog hates senior dog food.

I have tried transitioning him to senior dog food for years

He turns his nose up at it.

As long as he's still eating, is it harmful to feed him food for small dogs adult age 7+. ?

He eats Purina Pro Plan shredded. It seems to be his favorite.

I don't notice that much difference in the ingredients between adult and senior small breed dog food.

He will be 15 in March. I am dreading the day he doesn't want to eat anything anymore.