Michael Piller spent a few weeks mulling over ideas for the ninth Star Trek film. He and producer Rick Berman agreed that since the previous film First Contact had been so dark and featured an incredibly formidable villain in the Borg, it would probably be best to go in another direction.
They began with the idea of finding a public domain story to adapt into the Trek universe. Then, one morning Piller was making his daily application of Rogaine when it hit him that a fountain of youth story might be the right way to go. Wedding it to an adaptation of Heart of Darkness, he pitched an idea that had Picard sent on a mission to track down an old friend who has seemingly gone rogue. When he discovers his friend's hiding place, he's shocked to find the man looking as young as he did at the Academy.
The problem is that Berman hated it, and he had strong words for Piller: "Picard’s an old man who doesn’t get to buckle his swash until the planet makes him young again. But he’s our hero. When the movie’s over and he’s back to normal again, he needs to be a vital man of action. Patrick will hate this. He’ll never do it… You’re telling our star he’s an old man!”
Fact is, Stewart had no problem with the idea, and the Heart of Darkness plot would have been way more compelling than the slow, plodding revision. I love Patrick Stewart's take on the final plot:
In the story I have been reading this weekend we are enmeshed in a context of Federation politics, fine interpretations of The Prime Directive and ancient history – as ancient as Star Trek - of conflict between two members of The Federation. In the middle of all this there is a vaguely defined, characterless, uninteresting civilization who seem to have attended too many performances of Siegfried and Roy. [..] what I have read would have hardly composed a moderately interesting episode somewhere in the middle of season five of TNG.