Dandruff on back?

Hello, my little hamster has strange scales on his back and we've been watching and now the fur in that spot is gone. He's a bit older, which is why we thought that was the cause, but now it seems strange to me after reading a lot on the internet. Our vet doesn't open again until Monday. Can anyone help me? I'm a very loving animal person and it hurts my heart to see him like this. He's otherwise fine, he gets food and drinks regularly, runs on his wheel every now and then, but not often.