The following are my theories about Luke Skywalker's location before seeing Episode 7:
#1: After winning the war against the empire, Luke returned to planet Hoth and found the snow monster that captured him in episode 5. They talked through their differences and eventually fell in love, producing a litter of powerful Jedi snow monsters. Is this gross? Maybe. But not as gross as doing the same thing with his sister.
#2: Luke suffered from post war trauma and needed a way to deal with that, as anyone would if you found out your arch nemesis was your father who then risked his life in the end for you, after spending years trying to kill you and your friends. Understandable. To get through it, he moved to Endor and lives peacefully with the ewoks. Since ewoks are basically humanoid puppies, they had a similar effect on him as puppies on veterans i.e. helped rehabilitate him into a non-war lifestyle.
#3: Luke finally remembered when he passionately kissed his sister and needed to go digest that. Enough said.
After seeing episode 7:
Holy crap. What a great movie. All those theories were wrong but I have something more interesting to talk about. About six minutes into the movie, the fire alarm went off and the screen went black. Everyone groaned and got up to file out of the building. We were outside in the cold for five minutes, the firemen did their thing, and we went back inside. Mild annoyance, but not the end of the world. We go back in and sit in our seats. As everyone else is filing in, a guy starts freaking out. Two girls had taken his brother's seat and he was not happy about it. He started shouting at everyone and cursing. There were plenty of young children in theater (who were about to have their first Star Wars experience) so people were not cool with this guy cursing and scaring their kids. A different guy threw a punch at him and then it was mess of bodies and concerned theater goers. Finally, both people left the theater and we got to continue. There were a lot of emotions in that theater. Those people waited years to see a movie that was being delayed by a fire alarm and a random angry dude. That wasn't cool. But you know what was cool? The movie. I won't spoil anything, but it's worth your time and money. Go see it.