Both from your comment and the and the OP, it seems some part of America's higher employment rates is in jobs that are not particularly productive, nor really wanted very much by their participants.
On the other hand, all this data massaging still leaves France with real lower employment rates for young and old people. Especially the old part must include serious numbers of people willing and able to work who can't find it. That's a poblem no matter how you measure it.
I object to the term "data massaging" however. I don't think I'm doing anything the "specialists" don't do all the time, knowing that they are creating headline statistics that will be used by different links in the info and media chain to reinforce a world view. One in which the "free market economies" have proved that their way is not only the best but inevitable. When locusts move on, they leave nothing behind