That's a great question, Ron! A brand-new starter that's only days old won't perform as well as a starter that's fully mature. But by the time you get to measuring your starter's life in years, the only significant difference is the wonderful history associated with it. Over time, the yeasts in the flour you feed your starter as well as in the air around it will change its nature, so all starters are essentially unique local creations, and can indeed change in activity level and flavor over time. If you're looking for a more sour sourdough, the best thing you can do is focus on giving your dough a long and cold rise in the refrigerator. This will have much more of an impact on flavor than changing your starter will. Happy baking! 

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