In the wild blue-toungued skinks do brumate, and in captivity they need to brumate in order to breed. Some blue-toungues will go off feed for several weeks in the winter, but if you are not looking to breed them they do not need to be brumated. Just keep conditions constant and he will probably start to eat again soon. At this age I would even reccomend against brumating him. I usually wait until animals are at least a few years old to brumate them, and make sure that they have good body-weight and are in good health.