We're left with an embittered and alone Michael Corleone in 1968 at the end of II
I think it was 1960 or '61 at the latest, if we take the cue of Roth returning to the US to vote in the presidential election (1960). Neither he, nor Rocco (when he assassinated Roth, nor Michael brooding in the boathouse, looked eight years older than Roth did in Havana, and Michael and Rocco did in the penultimate boathouse scene where Michael has his kill-'em-all-and-humiliate-Tom scene.
