You see so many people Bidens age, walking around, shopping in supermarket, playing with their grandkids and no one says that they are old and fragile

There are healthy seniors and frail seniors and they can be the same age. Age has little to do with individual health. A lady I know just stopped driving. She turned 100 and decided she could just as easily order in her groceries. A fellow I know lost his license since he had advancing dementia at 71.