I can't buy him being over 31-35 in SF. Okay, a little - but it in my head it fits more. Of course, this is fiction and Marcone has displayed some slightly superhuman feats. He's extremely athletic.
Able to speed attack supernatural creatures with knife attacks, dodge an attacking flying Nicodemus, throw a knife through a rope, jump across a detaching train. He's done several things physically early in the series which points to him being younger.
Not to say someone upper middle aged and over can't be physically capable, but it catches up to you, does it not? Murphy for example - a big part about last book was her injury and her getting older. Harry and Murphy are about the same age - Marcone has anywhere from five to twenty years on them (we'll assume based on this thread) yet has consistently shown to have superior reflexes, physical prowess, and speed in some regards.