I do believe that when they refer to "older" potatoes, they do mean uncooked. As with many root vegetables, after potatoes have been dug they have a decent amount of sugars in them. As those potatoes sit, unused, the sugar slowly converts to starches making them more ideal for gnocchi. Potatoes can last quite a long time once dug. Heck, they were one of the foods still left, in the old days, at the end of a long hard winter, and before the spring crops were ready. The reason potatoes turn soft and sprout is that most people don't store their potatoes properly, in a cool, dark place. Your kitchen is not the ideal environment. As for the sugars turning to starches it can really be seen in corn on the cob. A just picked cob will be really sweet, but let that same cob (or one you picked the same day) sit for a few days and you will taste a huge difference in sweetness as the sugars turn to starch.
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