He missed a Slam a year from 2012-14, and now presumably in 2016, so that's four out of the last five years that he's missed at least one Slam. In the last seven Slams he's played in, he's only made the QF twice and not gone beyond that. So yeah, the clock is ticking. If everything aligns just right, he could still win a Slam, but his chances aren't better than 34-year old Roger, and may even be worse.