Hi Guitar, I have (4) 12 week old squirrels. They have reached the teenage stage. They can be quite naughty.
I plan to release them on Thanksgiving week. Of course, I'm in FL so November releases are common. My girls have weaned. They were getting spotty with their willingness to take a syringe so I stopped. They also used it as an opportunity to escape and run like fools. I give them formula in a bowl and they are taking it from a bowl. If yours is chewing the nipple I would try the bowl.
Because the HHB are a supplement block I would only give 2 blocks to a 12 week old. You could give a rodent block but I doubt he would eat it after tasting the HHB. I start mine on Harlan Teklad block and they eat it fine when that's all they know. I have been adding the HHB's now.
The nut question is problematic. I suppose a single squirrel could have A single nut as a treat. I can't give mine nuts as the introduction of nuts to a group causes them to fight. I don't want to encourage that right now so I'm holding off until they get in the release cage. Squirrels get a little cuckoo when a nut is involved. Don't let him store them as he will get aggressive protecting his stash. You could give him an in shell nut to file the teeth. It will occupy his time, file the teeth and satisfy the chewing desire. Again, I'm holding off with my gang of 4. They also enjoy chewing small branches from safe trees. I give them oak branches.