Directing may just seem like pointing and sitting behind monitors, but it is actually some very stressful work. Maybe some directors are able to make light of it and take it easy, but from documentaries and interviews, George seems to be one to get pretty stressed.
I never thought George was done with directing back in the eighties and nineites. This guy was suppose to be an amazing up and coming director, by the mid eighties he had just finished with Star Wars, and now was expected to get on with making the kinds of films he had wanted to make, because that is what he said he wanted to do after ROTJ was done.
I didn't expect him to direct the upcoming prequel trilogy, because he said he was going to hire a different director for each film, but I wasn't surprised when he changed his mind and did them himself. He never announced that he was retireing from the directors chair. I don't think anybody believed he never direct another movie again back then. Even back then he was talking about Red Tails.
I still don't think this prelude trilogy will ever happen, not saying it is impossible, but I highly doubt it. If it does get made, I imagine it will be at a day and an age when George doesn't have anything to do with it and the SW liscense has been opened up for others to play around with. Kind of like Star Trek.