Our local humane society has a Seniors For Seniors program. If a senior adopts a senior pet there is no adoption fee & the shots are free for the lifetime. Their idea of senior pet is still a relatively young. Most of my dogs are or are close to being "senior" & are as active as I can handle! My "senior" sheltie is as active as my neighbor's 3 year old golden retriever. My advice is to go on a case by case basis. Some young dogs will be lazier & have health issues that you'd expect a senior to have. Some seniors will be as active & healthy as younger dogs. Each one is different. I always say "never say never" .