Don't like either, but the only way McGregor even has a prayer is if Floyd didn't take him seriously and train. That's it. Age won't matter...he's so far and away better at boxing than McGregor that it just won't be a contest unless Floyd either didn't train or just does something stupid because he doesn't respect McGregor.
All advantages go to Floyd. Speed, quickness, punching power. Yes, punching power. He hits harder than Conor, who isn't huge on striking power.
Paulie Malignaggi, who was totally out of shape, sparred Conor twice. First time, Paulie says he was struggling with conditioning. Second time, after he worked for a week or so, they went 12 rounds and Paulie says he "beat Conor's ass". I believe him. And Paulie, admittedly, is no Floyd. If an out-of-shape Paulie beat Conor with a week's training, Floyd will destroy him. Unless, again...Floyd does something stupid. Which he's never done in a ring so far. 49 actual boxers have never been able to beat him, doubt that a converted UFC guy can.