Is there any parts of the body that age equally in all people no matter how fit you are?

The hands. Veins become prominent as the skin thins. many old famous actresses have beautiful botoxed faces, but look at their hands.

Not a single one, you name it and there are people with better ones and people with worse ones. 

My guess would be the bladder. "The older you are, the more likely you are to need to pee at night. As you age, your body produces less of a hormone that helps concentrate urine so that you can hold it until the morning." 

No, there is far too much variability in genetics, etc for that to be possible.

Sure,  lots.   Like collagen.   It begins to break down and there is no remedy nor preventing it.

That's why old people get saggy.

The outer ear.