Exactly what I ask in the title. My son which is 5 years old play the game with me every week. Admittedly we don't use asteroids, scenarios nor "real" placement. We just play on the table surface and I have had to strip down the rules a bit, and then adding on as we play more games.
He often makes banks and turns in the wrong direction in the late game (I guess it is hard for a 5 year old to chose arrow from the perspective of the ship, and not himself) and have problems understanding some advanced rule interaction, but I have used the game to have him train math (how many red Dice does your X-wing have?).
He also understand the difference between the orange, red, green, yellow and blue numbers on his cards. Of course he is involved in listbuilding, even though he chooses the things he thinks are cool (I want to have Chewbacca dad!) so there isn't very much powergaming in him yet.
He also just have gotten the hang of the differences between shooting at range 1, 2 and 3. He is very good at concentrating his fire (admittedly he loves Millenium Falcon and uses one 90% of the time, and I try to make his lists hard for me to beat so he often have Chewbacca with Luke or Han with Chewbacca and Gunner/Luke. This helps him concentrating his fire I think.)
As you might understand, he loves Star Wars. Interestingly I think he is still to young to Watch the real films, and he has only seen maybe 3-4 episodes of Clone Wars (since it's not ok to Watch it when he is with his Little sister, and in my opinion it is borderline too violent for a 5 year old too).
He also owns some Lego Star Wars and he loves to listen to my CD with the Music from Star Wars when going to bed. (This has the unexpected falout that his 2,5 years old sister often sings the Darth Vader theme, which my son hates by the way, since Darth Vader is an evil villain).
So, do you know any kid even younger who have played X-wing and how has it worked out?