Pondering that myself. My kid is 4, and his little friend at school has seen it thanks to an older sibling. So he's interested. CommonsenseMedia.org says 7, I'm not sure we'll make it that long.. I thought about cutting out the choke scene, the chard bodies and the torture droid and maybe it'd be okay after that.
Mom should start watching as soon as the little one is conceived.
My kids were 8 & 5 when they first watched Star Wars, but truthfully they were not that much into it that a year later they both have not asked to watch the next one or repeat Star Wars again. They do love the Lego game, though.
I like the idea of that movie order. Doesn't take the "Luke I am your father" surprise away.