sorry, this is going to be a little long.
I adopted my dog from a shelter and he doesn't seem to know how to play.
He's a 35lb mutt--supposedly husky mix--around 6-8 yrs old (looks kind of like a small tricolor lab mix). The shelter didn't have a background on him. Very well behaved, almost too well, doesn't bark, doesn't whine, doesn't pee in the house. He doesn't even run to the front door when someone other than me comes home.
I really want to encourage him to enjoy himself and play. He's shown no interest in chew toys, tennis balls, squeaky toys, and the only time he's interested in his kong is when treats are sticking out of it. If the treats require too much effort to get out, he'll simply leave it.
I've tried soaking tennis balls in gravy, covering them with peanut butter, and keeping one in his kibble bag. Nothing. he'll lick the tennis ball a bit and then leave it. I've gotten down on all four and nudge him with my head...playing with toys and he just stares at me, not even really look at the toys.
He's most energetic in the morning. He likes walks and other dogs but I haven't taken him to a dog park since he doesn't listen to "come here" when I call him (still working on that). When we get home and I have his food, I can get him excited enough (or maybe frustrated enough

) to dart around the room, crouching at his various spots and by my feet. When I feed his dinner and take him out for an evening walk, he'll get a little excited but not as much as in the morning. Training sessions with treats get him interested but otherwise he just sleeps.
I don't think he's just lazy and feel that he wants to play. We have a lot of wild rabbits in the area and he's tried to chased them a few times, though not every time he sees them. I've ran around with him at the park and he seems to love that. Problem is that I can't let him run off leash because he would run after other dogs to play or places to smell. Again, need to work on the come command. If I run with him on leash, he gets into that playful back and forth jog and I would trip over him. Almost rolled my ankle to avoid hitting him once

.
So is he just old? I don't really know what to do. He might have had a rough life before since it seems he's always having nightmares when he sleeps. Only time I've every heard him bark.
Training the come command will still take quite a while. He doesn't seem to learn quick and doesn't pay attention when outside. So I was hoping for some ideas of keeping him active and healthy. Thanks.