Mac just picked it up right away, it was fun at the beginning, but now it's just getting annoying.
He want's to play fetch at the worst times, like when I'm cooking or just trying to relax. And he'll bring every toy to you until you finally pick one up and toss it. The other weird thing that he knew how to do without me teaching it is getting him to bring his toy to me. One day he was whining, and I knew that he wanted to play, so I said "Where is your toy Mac?" and he quickly went searching for a toy to bring me, and he did! And he's been doing it ever since. Sometimes I hide the toys from him, and I see how long it will take to find them.
Good luck with the fetching though, I think eventually most dogs do it sooner or later.