We've had our Russian Dwarf hamster for 14 wks & he was 9 wks old when we got him. He settled in straight away & appears to be a very content, friendly, chubby little thing!
He happily comes out his bed when we call his name, probably because he thinks we've got a sunflower seed for him!
Anyway, his cage is what we bought when we got him & what was recommended for him so big enough. I made a little shelf for him on the opposide side of his bed, out of an empty shoe box, which he loves. Just recently though, he's been chewing at it, a lot! I don't think he's eating the cardboard as I can see bits of it in his cage. He does have one of those holey log things to gnaw on & a fruit& nut bar, so is he just 'gnawing' at the cardboard for enjoyment? It's funny how he never bothered beforehand & only started recently?! He seems fine otherwise.