Old Joe and young Joe are not also the kid, right?

right. the kid is the bad guy from the future that takes control.
young joe kills himself to prevent the kid from being evil, thus changing the future hopefully.

The kid is the rainmaker the one man army a totally separate character, and not an alternate version of the "Joes"

The voice over by Levitt confused me because of the kid on the train thing which was his experience as a child.

In this movie, it showed JGL and Willis's characters in separate timelines, which they would have to have done in order for them both to exist at the same point in one timeline; but we saw that everything that happened to JGL in his own timeline directly affected Willis (we see that in his 'fuzzy memories, physical scarring and of course the ending scene). With that said, Willis was sent back in time to be killed by the Rainmaker and his goal was to kill the Rainmaker as a child to save his future wife's life. That doesn't really make much sense though because Willis talking to/interacting with his past self (JGL) should have completely changed his future (and subsequently himself). We could tell that he was obviously falling in love with Sarah and likely would have pursued a relationship with her although he never even would have met her had Willis not gone back in time. Also, he was attempting to kill the Rainmaker, but if the Rainmaker weren't alive to take over the future, who knows when Willis would have been sent back to seal his loop? He could have ended up going to Shanghai 5 years later or earlier or whatever. There's no guarantee that he would have met his future wife anyway.

Is this making any sense? I don't know; it sounded much clearer in my head. I guess he wasn't lying when he said it was a "precise description of a fuzzy concept".

Whatever. If that doesn't make sense, I thought the telekinetic storyline was kind of out of place. Plus JGL's makeup ****ing blew. I guess they had to make him look more like a younger Bruce Willis but damn, they could have done better..

Also, why did they spend so much time showing JGL learning French and discussing his plans to go to France only for us to find out that (from Willis's timeline) he went straight to Shanghai for 'retirement'?