Adult leopard geckos can go months, especially if they go into brumation, which means that they go to the cool side and essentially sleep through the winter. One of my leopard geckos, that I've had for 10 years, frequently doesn't eat all winter. At his worst, he went from Nov. to May. This wasn't best for him, and he had a respiratory infection (which was treated after a vet visit), but he pulled through after losing about 20 grams. Now, in November, he's still eating (I expect he may stop in January) and weighs about 75 grams.
Aliza