The world's oldest sourdough?

Your sourdough starter is as old as its last feed. I don't agree with this. Starters are on-going and while certainly under a microscope the yeasts and bacteria will have all been replaced every feed or two the starter process is a continuous chain so on a macro scale it's the same starter. However, whenever this topic comes up there's always someone... If you have nurtured it continuously for many years then it's more than just the yeasts and bacteria. You've put your time and effort into it for however many years maintaining the same starter. 

Is a more elegant term for what used to be referred to as “backslopping” for tomorrow’s bread. It is however a pretty good way to describe what happens when I feed my starter late at night in a perfectly clean kitchen. I am thinking Pliny’s wife came up with that one;-)