How Do I Interest My Aussie In Fetching And Playing?

My Aussie Jack is a rescue dog about 18 month old. I have had him since November. When I got him he did not know what a toy was or a ball or anything playful.

No matter how many times I try to get him interested in playing with a toy, ball or frisbee, I get very little reaction. He will go (fetch) get the item when I get him real excited but he rarely brings it back.

He is very loving. He seems very smart sometimes and dumb as a brick other times.

How do I get him to be interested in fetching and playing so he can get better exercise?

Thank you,

Sylvia