I was at the shelter last, Fri, 10 to noon. That being my usual day & time to volunteer. Of the kitties that are currently available for adoption, we have one four year old & another that might be that age or a little older. Neither are seniors. As for the dogs, I don’t think we have any in that age range either.
Since cats can often live longer than dogs, especially if they’re indoor only, senior often starts for them at past 10. For many dogs, that age is their upper limit. So, being a senior for them is considered what the last 25% of their life is.
We have two senior kitties. Both 11. Though, the way they run around, chase & wrestle each other, you’d never know it. Do you have or have you had an older animal companion?