I'd get him checked out to rule out physical issues. A rabbit that age should be more active, but I imagine there are exceptions. Has he explored much in the past?
What is his area like? Does he have overhead cover, traction and a box or something to hide in? Anything in corner to hop up on or chew/shred/play with?
I have other homebodies but its usually because they really like their area, its large, lots of levels and traction and boxes full of hay, etc, and they're older. They make one round of the house when I open the door and then head back home.
Neil, my smashed leg guy, tends to stick to his corner or where there is overhead cover and a hiding box, although he'll check out a few things close by. (He was living in a thicket at UVic after being hit by a car). He may realize his disability makes that necessary. His pen mate is all over the house. (She was a park bunny).
One of the UVic offspring bunnies (born and raised indoors) is pretty shy and doesn't go very far, but the other five are curious in stages(the three black ones being the shyest, the colored ones less shy and the blonde ridiculously outgoing).
sas :bunnydance: