Anorexia, if that's what it is, can be very challenging. We took in two dragons about a year ago who had NEVER eaten on their own since the previous owner aquired them. It took two months of work to get them feeding and growing. They're fine now, but there were certainly times I felt discouraged.
I too would check the temperatures. They really do need the heat and light to stimulate feeding and digestion. Even 5-10 degrees up can make a big difference. And add an hour to the light cycle.
You say he hasn't grown lengthwise. Is he a good weight? Do you think he has gained or at least maintained his weight or does he seem scrawny? Has he had a bowel movement recently? Have you tried incorporating a probiotic into the regimine?
The other possibility is that he is trying to brumate. He sounds a little young for it, but sometimes they just insist. Do you think this might be the case?
I have two dragons missing several digits (One is missing an entire foot, among other things). Once healed, it really doesn't seem to bother them or inhibit their climbing. Maybe he misses climbing?
Taking in rescues (or rescuing by purchasing) can be very rewarding. It can also be a LOT of work and expense and be discouraging at times. If you feel you simply don't have the resources to deal with a special-needy animal right now is there somebody you know who might? Do you have a local herp society you might be able to use as a back-up?
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4.3 Bearded Dragons (Rescues)
1.0 Corn snake (Rescue)
0.1 California King
4.5 Royal (Ball) Pythons (3 rescues)
1.1 Dogs (Rescues)
2.0 Cats (Rescues)
2.2 Humans
No, it's NOT a big house