Federer has not won a slam since he was 28(January 2010) but somehow the less talented Djokovic and Murray will do what Federer has not been able to do in this physical era, win a slam after 28.
You never know. It could happen. Just because Federer hasn't managed to do it, doesn't mean no one else can. Didn't he play a Slam final last year? If he would have met someone not named Nadal in the final, he would have probably won RG. Winning a Slam depends on many factors, not just talent (which Djokovic and Murray already have).