Many bakers think that the older the starter the better. Well, it's not so. Sure, I'd like to be able to say my starter came from Ramses during the Third Dynasty, but it actually came from my kitchen 15 years ago. Your starter might be one week old or it might have been entrusted you by granny, but it's all irrelevant. The only thing that's important is that it's well-fed, healthy, robust and full of bubbles.
And nobody really knows for sure how starter becomes starter. Some say the wild yeast and bacteria that turn flour and water into starter come from the atmosphere, and then there are those who say the bacteria and wild yeast reside in the wheat. Finally, some say the magical wild yeasts and bacteria really come from the baker. Your choice.